diff --git a/proto/api/v1/instance_service.proto b/proto/api/v1/instance_service.proto
index 0b97bb827..418f4e1ce 100644
--- a/proto/api/v1/instance_service.proto
+++ b/proto/api/v1/instance_service.proto
@@ -83,9 +83,6 @@ message InstanceSetting {
 
   // General instance settings configuration.
   message GeneralSetting {
-    // theme is the name of the selected theme.
-    // This references a CSS file in the web/public/themes/ directory.
-    string theme = 1;
     // disallow_user_registration disallows user registration.
     bool disallow_user_registration = 2;
     // disallow_password_auth disallows password authentication.
@@ -111,7 +108,6 @@ message InstanceSetting {
       string title = 1;
       string description = 2;
       string logo_url = 3;
-      string locale = 4;
     }
   }
 
diff --git a/proto/gen/api/v1/activity_service_grpc.pb.go b/proto/gen/api/v1/activity_service_grpc.pb.go
index d9d0594ef..ee48c8471 100644
--- a/proto/gen/api/v1/activity_service_grpc.pb.go
+++ b/proto/gen/api/v1/activity_service_grpc.pb.go
@@ -1,6 +1,6 @@
 // Code generated by protoc-gen-go-grpc. DO NOT EDIT.
 // versions:
-// - protoc-gen-go-grpc v1.5.1
+// - protoc-gen-go-grpc v1.6.0
 // - protoc             (unknown)
 // source: api/v1/activity_service.proto
 
@@ -80,10 +80,10 @@ type ActivityServiceServer interface {
 type UnimplementedActivityServiceServer struct{}
 
 func (UnimplementedActivityServiceServer) ListActivities(context.Context, *ListActivitiesRequest) (*ListActivitiesResponse, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method ListActivities not implemented")
+	return nil, status.Error(codes.Unimplemented, "method ListActivities not implemented")
 }
 func (UnimplementedActivityServiceServer) GetActivity(context.Context, *GetActivityRequest) (*Activity, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method GetActivity not implemented")
+	return nil, status.Error(codes.Unimplemented, "method GetActivity not implemented")
 }
 func (UnimplementedActivityServiceServer) mustEmbedUnimplementedActivityServiceServer() {}
 func (UnimplementedActivityServiceServer) testEmbeddedByValue()                         {}
@@ -96,7 +96,7 @@ type UnsafeActivityServiceServer interface {
 }
 
 func RegisterActivityServiceServer(s grpc.ServiceRegistrar, srv ActivityServiceServer) {
-	// If the following call pancis, it indicates UnimplementedActivityServiceServer was
+	// If the following call panics, it indicates UnimplementedActivityServiceServer was
 	// embedded by pointer and is nil.  This will cause panics if an
 	// unimplemented method is ever invoked, so we test this at initialization
 	// time to prevent it from happening at runtime later due to I/O.
diff --git a/proto/gen/api/v1/attachment_service_grpc.pb.go b/proto/gen/api/v1/attachment_service_grpc.pb.go
index fa07861a3..a453128ea 100644
--- a/proto/gen/api/v1/attachment_service_grpc.pb.go
+++ b/proto/gen/api/v1/attachment_service_grpc.pb.go
@@ -1,6 +1,6 @@
 // Code generated by protoc-gen-go-grpc. DO NOT EDIT.
 // versions:
-// - protoc-gen-go-grpc v1.5.1
+// - protoc-gen-go-grpc v1.6.0
 // - protoc             (unknown)
 // source: api/v1/attachment_service.proto
 
@@ -142,22 +142,22 @@ type AttachmentServiceServer interface {
 type UnimplementedAttachmentServiceServer struct{}
 
 func (UnimplementedAttachmentServiceServer) CreateAttachment(context.Context, *CreateAttachmentRequest) (*Attachment, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method CreateAttachment not implemented")
+	return nil, status.Error(codes.Unimplemented, "method CreateAttachment not implemented")
 }
 func (UnimplementedAttachmentServiceServer) ListAttachments(context.Context, *ListAttachmentsRequest) (*ListAttachmentsResponse, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method ListAttachments not implemented")
+	return nil, status.Error(codes.Unimplemented, "method ListAttachments not implemented")
 }
 func (UnimplementedAttachmentServiceServer) GetAttachment(context.Context, *GetAttachmentRequest) (*Attachment, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method GetAttachment not implemented")
+	return nil, status.Error(codes.Unimplemented, "method GetAttachment not implemented")
 }
 func (UnimplementedAttachmentServiceServer) GetAttachmentBinary(context.Context, *GetAttachmentBinaryRequest) (*httpbody.HttpBody, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method GetAttachmentBinary not implemented")
+	return nil, status.Error(codes.Unimplemented, "method GetAttachmentBinary not implemented")
 }
 func (UnimplementedAttachmentServiceServer) UpdateAttachment(context.Context, *UpdateAttachmentRequest) (*Attachment, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method UpdateAttachment not implemented")
+	return nil, status.Error(codes.Unimplemented, "method UpdateAttachment not implemented")
 }
 func (UnimplementedAttachmentServiceServer) DeleteAttachment(context.Context, *DeleteAttachmentRequest) (*emptypb.Empty, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method DeleteAttachment not implemented")
+	return nil, status.Error(codes.Unimplemented, "method DeleteAttachment not implemented")
 }
 func (UnimplementedAttachmentServiceServer) mustEmbedUnimplementedAttachmentServiceServer() {}
 func (UnimplementedAttachmentServiceServer) testEmbeddedByValue()                           {}
@@ -170,7 +170,7 @@ type UnsafeAttachmentServiceServer interface {
 }
 
 func RegisterAttachmentServiceServer(s grpc.ServiceRegistrar, srv AttachmentServiceServer) {
-	// If the following call pancis, it indicates UnimplementedAttachmentServiceServer was
+	// If the following call panics, it indicates UnimplementedAttachmentServiceServer was
 	// embedded by pointer and is nil.  This will cause panics if an
 	// unimplemented method is ever invoked, so we test this at initialization
 	// time to prevent it from happening at runtime later due to I/O.
diff --git a/proto/gen/api/v1/auth_service_grpc.pb.go b/proto/gen/api/v1/auth_service_grpc.pb.go
index 2872b28be..9f6555643 100644
--- a/proto/gen/api/v1/auth_service_grpc.pb.go
+++ b/proto/gen/api/v1/auth_service_grpc.pb.go
@@ -1,6 +1,6 @@
 // Code generated by protoc-gen-go-grpc. DO NOT EDIT.
 // versions:
-// - protoc-gen-go-grpc v1.5.1
+// - protoc-gen-go-grpc v1.6.0
 // - protoc             (unknown)
 // source: api/v1/auth_service.proto
 
@@ -102,13 +102,13 @@ type AuthServiceServer interface {
 type UnimplementedAuthServiceServer struct{}
 
 func (UnimplementedAuthServiceServer) GetCurrentSession(context.Context, *GetCurrentSessionRequest) (*GetCurrentSessionResponse, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method GetCurrentSession not implemented")
+	return nil, status.Error(codes.Unimplemented, "method GetCurrentSession not implemented")
 }
 func (UnimplementedAuthServiceServer) CreateSession(context.Context, *CreateSessionRequest) (*CreateSessionResponse, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method CreateSession not implemented")
+	return nil, status.Error(codes.Unimplemented, "method CreateSession not implemented")
 }
 func (UnimplementedAuthServiceServer) DeleteSession(context.Context, *DeleteSessionRequest) (*emptypb.Empty, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method DeleteSession not implemented")
+	return nil, status.Error(codes.Unimplemented, "method DeleteSession not implemented")
 }
 func (UnimplementedAuthServiceServer) mustEmbedUnimplementedAuthServiceServer() {}
 func (UnimplementedAuthServiceServer) testEmbeddedByValue()                     {}
@@ -121,7 +121,7 @@ type UnsafeAuthServiceServer interface {
 }
 
 func RegisterAuthServiceServer(s grpc.ServiceRegistrar, srv AuthServiceServer) {
-	// If the following call pancis, it indicates UnimplementedAuthServiceServer was
+	// If the following call panics, it indicates UnimplementedAuthServiceServer was
 	// embedded by pointer and is nil.  This will cause panics if an
 	// unimplemented method is ever invoked, so we test this at initialization
 	// time to prevent it from happening at runtime later due to I/O.
diff --git a/proto/gen/api/v1/idp_service_grpc.pb.go b/proto/gen/api/v1/idp_service_grpc.pb.go
index 3a9bee2e5..bce241228 100644
--- a/proto/gen/api/v1/idp_service_grpc.pb.go
+++ b/proto/gen/api/v1/idp_service_grpc.pb.go
@@ -1,6 +1,6 @@
 // Code generated by protoc-gen-go-grpc. DO NOT EDIT.
 // versions:
-// - protoc-gen-go-grpc v1.5.1
+// - protoc-gen-go-grpc v1.6.0
 // - protoc             (unknown)
 // source: api/v1/idp_service.proto
 
@@ -126,19 +126,19 @@ type IdentityProviderServiceServer interface {
 type UnimplementedIdentityProviderServiceServer struct{}
 
 func (UnimplementedIdentityProviderServiceServer) ListIdentityProviders(context.Context, *ListIdentityProvidersRequest) (*ListIdentityProvidersResponse, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method ListIdentityProviders not implemented")
+	return nil, status.Error(codes.Unimplemented, "method ListIdentityProviders not implemented")
 }
 func (UnimplementedIdentityProviderServiceServer) GetIdentityProvider(context.Context, *GetIdentityProviderRequest) (*IdentityProvider, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method GetIdentityProvider not implemented")
+	return nil, status.Error(codes.Unimplemented, "method GetIdentityProvider not implemented")
 }
 func (UnimplementedIdentityProviderServiceServer) CreateIdentityProvider(context.Context, *CreateIdentityProviderRequest) (*IdentityProvider, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method CreateIdentityProvider not implemented")
+	return nil, status.Error(codes.Unimplemented, "method CreateIdentityProvider not implemented")
 }
 func (UnimplementedIdentityProviderServiceServer) UpdateIdentityProvider(context.Context, *UpdateIdentityProviderRequest) (*IdentityProvider, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method UpdateIdentityProvider not implemented")
+	return nil, status.Error(codes.Unimplemented, "method UpdateIdentityProvider not implemented")
 }
 func (UnimplementedIdentityProviderServiceServer) DeleteIdentityProvider(context.Context, *DeleteIdentityProviderRequest) (*emptypb.Empty, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method DeleteIdentityProvider not implemented")
+	return nil, status.Error(codes.Unimplemented, "method DeleteIdentityProvider not implemented")
 }
 func (UnimplementedIdentityProviderServiceServer) mustEmbedUnimplementedIdentityProviderServiceServer() {
 }
@@ -152,7 +152,7 @@ type UnsafeIdentityProviderServiceServer interface {
 }
 
 func RegisterIdentityProviderServiceServer(s grpc.ServiceRegistrar, srv IdentityProviderServiceServer) {
-	// If the following call pancis, it indicates UnimplementedIdentityProviderServiceServer was
+	// If the following call panics, it indicates UnimplementedIdentityProviderServiceServer was
 	// embedded by pointer and is nil.  This will cause panics if an
 	// unimplemented method is ever invoked, so we test this at initialization
 	// time to prevent it from happening at runtime later due to I/O.
diff --git a/proto/gen/api/v1/instance_service.pb.go b/proto/gen/api/v1/instance_service.pb.go
index 248d18be2..71b72df83 100644
--- a/proto/gen/api/v1/instance_service.pb.go
+++ b/proto/gen/api/v1/instance_service.pb.go
@@ -460,9 +460,6 @@ func (x *UpdateInstanceSettingRequest) GetUpdateMask() *fieldmaskpb.FieldMask {
 // General instance settings configuration.
 type InstanceSetting_GeneralSetting struct {
 	state protoimpl.MessageState `protogen:"open.v1"`
-	// theme is the name of the selected theme.
-	// This references a CSS file in the web/public/themes/ directory.
-	Theme string `protobuf:"bytes,1,opt,name=theme,proto3" json:"theme,omitempty"`
 	// disallow_user_registration disallows user registration.
 	DisallowUserRegistration bool `protobuf:"varint,2,opt,name=disallow_user_registration,json=disallowUserRegistration,proto3" json:"disallow_user_registration,omitempty"`
 	// disallow_password_auth disallows password authentication.
@@ -515,13 +512,6 @@ func (*InstanceSetting_GeneralSetting) Descriptor() ([]byte, []int) {
 	return file_api_v1_instance_service_proto_rawDescGZIP(), []int{2, 0}
 }
 
-func (x *InstanceSetting_GeneralSetting) GetTheme() string {
-	if x != nil {
-		return x.Theme
-	}
-	return ""
-}
-
 func (x *InstanceSetting_GeneralSetting) GetDisallowUserRegistration() bool {
 	if x != nil {
 		return x.DisallowUserRegistration
@@ -758,7 +748,6 @@ type InstanceSetting_GeneralSetting_CustomProfile struct {
 	Title         string                 `protobuf:"bytes,1,opt,name=title,proto3" json:"title,omitempty"`
 	Description   string                 `protobuf:"bytes,2,opt,name=description,proto3" json:"description,omitempty"`
 	LogoUrl       string                 `protobuf:"bytes,3,opt,name=logo_url,json=logoUrl,proto3" json:"logo_url,omitempty"`
-	Locale        string                 `protobuf:"bytes,4,opt,name=locale,proto3" json:"locale,omitempty"`
 	unknownFields protoimpl.UnknownFields
 	sizeCache     protoimpl.SizeCache
 }
@@ -814,13 +803,6 @@ func (x *InstanceSetting_GeneralSetting_CustomProfile) GetLogoUrl() string {
 	return ""
 }
 
-func (x *InstanceSetting_GeneralSetting_CustomProfile) GetLocale() string {
-	if x != nil {
-		return x.Locale
-	}
-	return ""
-}
-
 // S3 configuration for cloud storage backend.
 // Reference: https://developers.cloudflare.com/r2/examples/aws/aws-sdk-go/
 type InstanceSetting_StorageSetting_S3Config struct {
@@ -917,14 +899,13 @@ const file_api_v1_instance_service_proto_rawDesc = "" +
 	"\aversion\x18\x02 \x01(\tR\aversion\x12\x12\n" +
 	"\x04mode\x18\x03 \x01(\tR\x04mode\x12!\n" +
 	"\finstance_url\x18\x06 \x01(\tR\vinstanceUrl\"\x1b\n" +
-	"\x19GetInstanceProfileRequest\"\x9d\x10\n" +
+	"\x19GetInstanceProfileRequest\"\xef\x0f\n" +
 	"\x0fInstanceSetting\x12\x17\n" +
 	"\x04name\x18\x01 \x01(\tB\x03\xe0A\bR\x04name\x12W\n" +
 	"\x0fgeneral_setting\x18\x02 \x01(\v2,.memos.api.v1.InstanceSetting.GeneralSettingH\x00R\x0egeneralSetting\x12W\n" +
 	"\x0fstorage_setting\x18\x03 \x01(\v2,.memos.api.v1.InstanceSetting.StorageSettingH\x00R\x0estorageSetting\x12d\n" +
-	"\x14memo_related_setting\x18\x04 \x01(\v20.memos.api.v1.InstanceSetting.MemoRelatedSettingH\x00R\x12memoRelatedSetting\x1a\xf8\x04\n" +
-	"\x0eGeneralSetting\x12\x14\n" +
-	"\x05theme\x18\x01 \x01(\tR\x05theme\x12<\n" +
+	"\x14memo_related_setting\x18\x04 \x01(\v20.memos.api.v1.InstanceSetting.MemoRelatedSettingH\x00R\x12memoRelatedSetting\x1a\xca\x04\n" +
+	"\x0eGeneralSetting\x12<\n" +
 	"\x1adisallow_user_registration\x18\x02 \x01(\bR\x18disallowUserRegistration\x124\n" +
 	"\x16disallow_password_auth\x18\x03 \x01(\bR\x14disallowPasswordAuth\x12+\n" +
 	"\x11additional_script\x18\x04 \x01(\tR\x10additionalScript\x12)\n" +
@@ -932,12 +913,11 @@ const file_api_v1_instance_service_proto_rawDesc = "" +
 	"\x0ecustom_profile\x18\x06 \x01(\v2:.memos.api.v1.InstanceSetting.GeneralSetting.CustomProfileR\rcustomProfile\x121\n" +
 	"\x15week_start_day_offset\x18\a \x01(\x05R\x12weekStartDayOffset\x128\n" +
 	"\x18disallow_change_username\x18\b \x01(\bR\x16disallowChangeUsername\x128\n" +
-	"\x18disallow_change_nickname\x18\t \x01(\bR\x16disallowChangeNickname\x1az\n" +
+	"\x18disallow_change_nickname\x18\t \x01(\bR\x16disallowChangeNickname\x1ab\n" +
 	"\rCustomProfile\x12\x14\n" +
 	"\x05title\x18\x01 \x01(\tR\x05title\x12 \n" +
 	"\vdescription\x18\x02 \x01(\tR\vdescription\x12\x19\n" +
-	"\blogo_url\x18\x03 \x01(\tR\alogoUrl\x12\x16\n" +
-	"\x06locale\x18\x04 \x01(\tR\x06locale\x1a\xbc\x04\n" +
+	"\blogo_url\x18\x03 \x01(\tR\alogoUrl\x1a\xbc\x04\n" +
 	"\x0eStorageSetting\x12[\n" +
 	"\fstorage_type\x18\x01 \x01(\x0e28.memos.api.v1.InstanceSetting.StorageSetting.StorageTypeR\vstorageType\x12+\n" +
 	"\x11filepath_template\x18\x02 \x01(\tR\x10filepathTemplate\x12/\n" +
diff --git a/proto/gen/api/v1/instance_service_grpc.pb.go b/proto/gen/api/v1/instance_service_grpc.pb.go
index a8d544f53..aaa18dd3e 100644
--- a/proto/gen/api/v1/instance_service_grpc.pb.go
+++ b/proto/gen/api/v1/instance_service_grpc.pb.go
@@ -1,6 +1,6 @@
 // Code generated by protoc-gen-go-grpc. DO NOT EDIT.
 // versions:
-// - protoc-gen-go-grpc v1.5.1
+// - protoc-gen-go-grpc v1.6.0
 // - protoc             (unknown)
 // source: api/v1/instance_service.proto
 
@@ -95,13 +95,13 @@ type InstanceServiceServer interface {
 type UnimplementedInstanceServiceServer struct{}
 
 func (UnimplementedInstanceServiceServer) GetInstanceProfile(context.Context, *GetInstanceProfileRequest) (*InstanceProfile, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method GetInstanceProfile not implemented")
+	return nil, status.Error(codes.Unimplemented, "method GetInstanceProfile not implemented")
 }
 func (UnimplementedInstanceServiceServer) GetInstanceSetting(context.Context, *GetInstanceSettingRequest) (*InstanceSetting, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method GetInstanceSetting not implemented")
+	return nil, status.Error(codes.Unimplemented, "method GetInstanceSetting not implemented")
 }
 func (UnimplementedInstanceServiceServer) UpdateInstanceSetting(context.Context, *UpdateInstanceSettingRequest) (*InstanceSetting, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method UpdateInstanceSetting not implemented")
+	return nil, status.Error(codes.Unimplemented, "method UpdateInstanceSetting not implemented")
 }
 func (UnimplementedInstanceServiceServer) mustEmbedUnimplementedInstanceServiceServer() {}
 func (UnimplementedInstanceServiceServer) testEmbeddedByValue()                         {}
@@ -114,7 +114,7 @@ type UnsafeInstanceServiceServer interface {
 }
 
 func RegisterInstanceServiceServer(s grpc.ServiceRegistrar, srv InstanceServiceServer) {
-	// If the following call pancis, it indicates UnimplementedInstanceServiceServer was
+	// If the following call panics, it indicates UnimplementedInstanceServiceServer was
 	// embedded by pointer and is nil.  This will cause panics if an
 	// unimplemented method is ever invoked, so we test this at initialization
 	// time to prevent it from happening at runtime later due to I/O.
diff --git a/proto/gen/api/v1/memo_service_grpc.pb.go b/proto/gen/api/v1/memo_service_grpc.pb.go
index 2e4e91815..a7d4f46e8 100644
--- a/proto/gen/api/v1/memo_service_grpc.pb.go
+++ b/proto/gen/api/v1/memo_service_grpc.pb.go
@@ -1,6 +1,6 @@
 // Code generated by protoc-gen-go-grpc. DO NOT EDIT.
 // versions:
-// - protoc-gen-go-grpc v1.5.1
+// - protoc-gen-go-grpc v1.6.0
 // - protoc             (unknown)
 // source: api/v1/memo_service.proto
 
@@ -261,46 +261,46 @@ type MemoServiceServer interface {
 type UnimplementedMemoServiceServer struct{}
 
 func (UnimplementedMemoServiceServer) CreateMemo(context.Context, *CreateMemoRequest) (*Memo, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method CreateMemo not implemented")
+	return nil, status.Error(codes.Unimplemented, "method CreateMemo not implemented")
 }
 func (UnimplementedMemoServiceServer) ListMemos(context.Context, *ListMemosRequest) (*ListMemosResponse, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method ListMemos not implemented")
+	return nil, status.Error(codes.Unimplemented, "method ListMemos not implemented")
 }
 func (UnimplementedMemoServiceServer) GetMemo(context.Context, *GetMemoRequest) (*Memo, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method GetMemo not implemented")
+	return nil, status.Error(codes.Unimplemented, "method GetMemo not implemented")
 }
 func (UnimplementedMemoServiceServer) UpdateMemo(context.Context, *UpdateMemoRequest) (*Memo, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method UpdateMemo not implemented")
+	return nil, status.Error(codes.Unimplemented, "method UpdateMemo not implemented")
 }
 func (UnimplementedMemoServiceServer) DeleteMemo(context.Context, *DeleteMemoRequest) (*emptypb.Empty, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method DeleteMemo not implemented")
+	return nil, status.Error(codes.Unimplemented, "method DeleteMemo not implemented")
 }
 func (UnimplementedMemoServiceServer) SetMemoAttachments(context.Context, *SetMemoAttachmentsRequest) (*emptypb.Empty, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method SetMemoAttachments not implemented")
+	return nil, status.Error(codes.Unimplemented, "method SetMemoAttachments not implemented")
 }
 func (UnimplementedMemoServiceServer) ListMemoAttachments(context.Context, *ListMemoAttachmentsRequest) (*ListMemoAttachmentsResponse, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method ListMemoAttachments not implemented")
+	return nil, status.Error(codes.Unimplemented, "method ListMemoAttachments not implemented")
 }
 func (UnimplementedMemoServiceServer) SetMemoRelations(context.Context, *SetMemoRelationsRequest) (*emptypb.Empty, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method SetMemoRelations not implemented")
+	return nil, status.Error(codes.Unimplemented, "method SetMemoRelations not implemented")
 }
 func (UnimplementedMemoServiceServer) ListMemoRelations(context.Context, *ListMemoRelationsRequest) (*ListMemoRelationsResponse, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method ListMemoRelations not implemented")
+	return nil, status.Error(codes.Unimplemented, "method ListMemoRelations not implemented")
 }
 func (UnimplementedMemoServiceServer) CreateMemoComment(context.Context, *CreateMemoCommentRequest) (*Memo, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method CreateMemoComment not implemented")
+	return nil, status.Error(codes.Unimplemented, "method CreateMemoComment not implemented")
 }
 func (UnimplementedMemoServiceServer) ListMemoComments(context.Context, *ListMemoCommentsRequest) (*ListMemoCommentsResponse, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method ListMemoComments not implemented")
+	return nil, status.Error(codes.Unimplemented, "method ListMemoComments not implemented")
 }
 func (UnimplementedMemoServiceServer) ListMemoReactions(context.Context, *ListMemoReactionsRequest) (*ListMemoReactionsResponse, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method ListMemoReactions not implemented")
+	return nil, status.Error(codes.Unimplemented, "method ListMemoReactions not implemented")
 }
 func (UnimplementedMemoServiceServer) UpsertMemoReaction(context.Context, *UpsertMemoReactionRequest) (*Reaction, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method UpsertMemoReaction not implemented")
+	return nil, status.Error(codes.Unimplemented, "method UpsertMemoReaction not implemented")
 }
 func (UnimplementedMemoServiceServer) DeleteMemoReaction(context.Context, *DeleteMemoReactionRequest) (*emptypb.Empty, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method DeleteMemoReaction not implemented")
+	return nil, status.Error(codes.Unimplemented, "method DeleteMemoReaction not implemented")
 }
 func (UnimplementedMemoServiceServer) mustEmbedUnimplementedMemoServiceServer() {}
 func (UnimplementedMemoServiceServer) testEmbeddedByValue()                     {}
@@ -313,7 +313,7 @@ type UnsafeMemoServiceServer interface {
 }
 
 func RegisterMemoServiceServer(s grpc.ServiceRegistrar, srv MemoServiceServer) {
-	// If the following call pancis, it indicates UnimplementedMemoServiceServer was
+	// If the following call panics, it indicates UnimplementedMemoServiceServer was
 	// embedded by pointer and is nil.  This will cause panics if an
 	// unimplemented method is ever invoked, so we test this at initialization
 	// time to prevent it from happening at runtime later due to I/O.
diff --git a/proto/gen/api/v1/shortcut_service_grpc.pb.go b/proto/gen/api/v1/shortcut_service_grpc.pb.go
index 3a3f5b89e..f6913ef07 100644
--- a/proto/gen/api/v1/shortcut_service_grpc.pb.go
+++ b/proto/gen/api/v1/shortcut_service_grpc.pb.go
@@ -1,6 +1,6 @@
 // Code generated by protoc-gen-go-grpc. DO NOT EDIT.
 // versions:
-// - protoc-gen-go-grpc v1.5.1
+// - protoc-gen-go-grpc v1.6.0
 // - protoc             (unknown)
 // source: api/v1/shortcut_service.proto
 
@@ -126,19 +126,19 @@ type ShortcutServiceServer interface {
 type UnimplementedShortcutServiceServer struct{}
 
 func (UnimplementedShortcutServiceServer) ListShortcuts(context.Context, *ListShortcutsRequest) (*ListShortcutsResponse, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method ListShortcuts not implemented")
+	return nil, status.Error(codes.Unimplemented, "method ListShortcuts not implemented")
 }
 func (UnimplementedShortcutServiceServer) GetShortcut(context.Context, *GetShortcutRequest) (*Shortcut, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method GetShortcut not implemented")
+	return nil, status.Error(codes.Unimplemented, "method GetShortcut not implemented")
 }
 func (UnimplementedShortcutServiceServer) CreateShortcut(context.Context, *CreateShortcutRequest) (*Shortcut, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method CreateShortcut not implemented")
+	return nil, status.Error(codes.Unimplemented, "method CreateShortcut not implemented")
 }
 func (UnimplementedShortcutServiceServer) UpdateShortcut(context.Context, *UpdateShortcutRequest) (*Shortcut, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method UpdateShortcut not implemented")
+	return nil, status.Error(codes.Unimplemented, "method UpdateShortcut not implemented")
 }
 func (UnimplementedShortcutServiceServer) DeleteShortcut(context.Context, *DeleteShortcutRequest) (*emptypb.Empty, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method DeleteShortcut not implemented")
+	return nil, status.Error(codes.Unimplemented, "method DeleteShortcut not implemented")
 }
 func (UnimplementedShortcutServiceServer) mustEmbedUnimplementedShortcutServiceServer() {}
 func (UnimplementedShortcutServiceServer) testEmbeddedByValue()                         {}
@@ -151,7 +151,7 @@ type UnsafeShortcutServiceServer interface {
 }
 
 func RegisterShortcutServiceServer(s grpc.ServiceRegistrar, srv ShortcutServiceServer) {
-	// If the following call pancis, it indicates UnimplementedShortcutServiceServer was
+	// If the following call panics, it indicates UnimplementedShortcutServiceServer was
 	// embedded by pointer and is nil.  This will cause panics if an
 	// unimplemented method is ever invoked, so we test this at initialization
 	// time to prevent it from happening at runtime later due to I/O.
diff --git a/proto/gen/api/v1/user_service_grpc.pb.go b/proto/gen/api/v1/user_service_grpc.pb.go
index 1d6527406..5f54cba22 100644
--- a/proto/gen/api/v1/user_service_grpc.pb.go
+++ b/proto/gen/api/v1/user_service_grpc.pb.go
@@ -1,6 +1,6 @@
 // Code generated by protoc-gen-go-grpc. DO NOT EDIT.
 // versions:
-// - protoc-gen-go-grpc v1.5.1
+// - protoc-gen-go-grpc v1.6.0
 // - protoc             (unknown)
 // source: api/v1/user_service.proto
 
@@ -403,73 +403,73 @@ type UserServiceServer interface {
 type UnimplementedUserServiceServer struct{}
 
 func (UnimplementedUserServiceServer) ListUsers(context.Context, *ListUsersRequest) (*ListUsersResponse, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method ListUsers not implemented")
+	return nil, status.Error(codes.Unimplemented, "method ListUsers not implemented")
 }
 func (UnimplementedUserServiceServer) GetUser(context.Context, *GetUserRequest) (*User, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method GetUser not implemented")
+	return nil, status.Error(codes.Unimplemented, "method GetUser not implemented")
 }
 func (UnimplementedUserServiceServer) CreateUser(context.Context, *CreateUserRequest) (*User, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method CreateUser not implemented")
+	return nil, status.Error(codes.Unimplemented, "method CreateUser not implemented")
 }
 func (UnimplementedUserServiceServer) UpdateUser(context.Context, *UpdateUserRequest) (*User, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method UpdateUser not implemented")
+	return nil, status.Error(codes.Unimplemented, "method UpdateUser not implemented")
 }
 func (UnimplementedUserServiceServer) DeleteUser(context.Context, *DeleteUserRequest) (*emptypb.Empty, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method DeleteUser not implemented")
+	return nil, status.Error(codes.Unimplemented, "method DeleteUser not implemented")
 }
 func (UnimplementedUserServiceServer) GetUserAvatar(context.Context, *GetUserAvatarRequest) (*httpbody.HttpBody, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method GetUserAvatar not implemented")
+	return nil, status.Error(codes.Unimplemented, "method GetUserAvatar not implemented")
 }
 func (UnimplementedUserServiceServer) ListAllUserStats(context.Context, *ListAllUserStatsRequest) (*ListAllUserStatsResponse, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method ListAllUserStats not implemented")
+	return nil, status.Error(codes.Unimplemented, "method ListAllUserStats not implemented")
 }
 func (UnimplementedUserServiceServer) GetUserStats(context.Context, *GetUserStatsRequest) (*UserStats, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method GetUserStats not implemented")
+	return nil, status.Error(codes.Unimplemented, "method GetUserStats not implemented")
 }
 func (UnimplementedUserServiceServer) GetUserSetting(context.Context, *GetUserSettingRequest) (*UserSetting, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method GetUserSetting not implemented")
+	return nil, status.Error(codes.Unimplemented, "method GetUserSetting not implemented")
 }
 func (UnimplementedUserServiceServer) UpdateUserSetting(context.Context, *UpdateUserSettingRequest) (*UserSetting, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method UpdateUserSetting not implemented")
+	return nil, status.Error(codes.Unimplemented, "method UpdateUserSetting not implemented")
 }
 func (UnimplementedUserServiceServer) ListUserSettings(context.Context, *ListUserSettingsRequest) (*ListUserSettingsResponse, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method ListUserSettings not implemented")
+	return nil, status.Error(codes.Unimplemented, "method ListUserSettings not implemented")
 }
 func (UnimplementedUserServiceServer) ListUserAccessTokens(context.Context, *ListUserAccessTokensRequest) (*ListUserAccessTokensResponse, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method ListUserAccessTokens not implemented")
+	return nil, status.Error(codes.Unimplemented, "method ListUserAccessTokens not implemented")
 }
 func (UnimplementedUserServiceServer) CreateUserAccessToken(context.Context, *CreateUserAccessTokenRequest) (*UserAccessToken, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method CreateUserAccessToken not implemented")
+	return nil, status.Error(codes.Unimplemented, "method CreateUserAccessToken not implemented")
 }
 func (UnimplementedUserServiceServer) DeleteUserAccessToken(context.Context, *DeleteUserAccessTokenRequest) (*emptypb.Empty, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method DeleteUserAccessToken not implemented")
+	return nil, status.Error(codes.Unimplemented, "method DeleteUserAccessToken not implemented")
 }
 func (UnimplementedUserServiceServer) ListUserSessions(context.Context, *ListUserSessionsRequest) (*ListUserSessionsResponse, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method ListUserSessions not implemented")
+	return nil, status.Error(codes.Unimplemented, "method ListUserSessions not implemented")
 }
 func (UnimplementedUserServiceServer) RevokeUserSession(context.Context, *RevokeUserSessionRequest) (*emptypb.Empty, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method RevokeUserSession not implemented")
+	return nil, status.Error(codes.Unimplemented, "method RevokeUserSession not implemented")
 }
 func (UnimplementedUserServiceServer) ListUserWebhooks(context.Context, *ListUserWebhooksRequest) (*ListUserWebhooksResponse, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method ListUserWebhooks not implemented")
+	return nil, status.Error(codes.Unimplemented, "method ListUserWebhooks not implemented")
 }
 func (UnimplementedUserServiceServer) CreateUserWebhook(context.Context, *CreateUserWebhookRequest) (*UserWebhook, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method CreateUserWebhook not implemented")
+	return nil, status.Error(codes.Unimplemented, "method CreateUserWebhook not implemented")
 }
 func (UnimplementedUserServiceServer) UpdateUserWebhook(context.Context, *UpdateUserWebhookRequest) (*UserWebhook, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method UpdateUserWebhook not implemented")
+	return nil, status.Error(codes.Unimplemented, "method UpdateUserWebhook not implemented")
 }
 func (UnimplementedUserServiceServer) DeleteUserWebhook(context.Context, *DeleteUserWebhookRequest) (*emptypb.Empty, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method DeleteUserWebhook not implemented")
+	return nil, status.Error(codes.Unimplemented, "method DeleteUserWebhook not implemented")
 }
 func (UnimplementedUserServiceServer) ListUserNotifications(context.Context, *ListUserNotificationsRequest) (*ListUserNotificationsResponse, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method ListUserNotifications not implemented")
+	return nil, status.Error(codes.Unimplemented, "method ListUserNotifications not implemented")
 }
 func (UnimplementedUserServiceServer) UpdateUserNotification(context.Context, *UpdateUserNotificationRequest) (*UserNotification, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method UpdateUserNotification not implemented")
+	return nil, status.Error(codes.Unimplemented, "method UpdateUserNotification not implemented")
 }
 func (UnimplementedUserServiceServer) DeleteUserNotification(context.Context, *DeleteUserNotificationRequest) (*emptypb.Empty, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method DeleteUserNotification not implemented")
+	return nil, status.Error(codes.Unimplemented, "method DeleteUserNotification not implemented")
 }
 func (UnimplementedUserServiceServer) mustEmbedUnimplementedUserServiceServer() {}
 func (UnimplementedUserServiceServer) testEmbeddedByValue()                     {}
@@ -482,7 +482,7 @@ type UnsafeUserServiceServer interface {
 }
 
 func RegisterUserServiceServer(s grpc.ServiceRegistrar, srv UserServiceServer) {
-	// If the following call pancis, it indicates UnimplementedUserServiceServer was
+	// If the following call panics, it indicates UnimplementedUserServiceServer was
 	// embedded by pointer and is nil.  This will cause panics if an
 	// unimplemented method is ever invoked, so we test this at initialization
 	// time to prevent it from happening at runtime later due to I/O.
diff --git a/proto/gen/openapi.yaml b/proto/gen/openapi.yaml
index ca0b288e9..0bd250136 100644
--- a/proto/gen/openapi.yaml
+++ b/proto/gen/openapi.yaml
@@ -2198,8 +2198,6 @@ components:
                     type: string
                 logoUrl:
                     type: string
-                locale:
-                    type: string
             description: Custom profile configuration for instance branding.
         GetCurrentSessionResponse:
             type: object
@@ -2290,11 +2288,6 @@ components:
         InstanceSetting_GeneralSetting:
             type: object
             properties:
-                theme:
-                    type: string
-                    description: |-
-                        theme is the name of the selected theme.
-                         This references a CSS file in the web/public/themes/ directory.
                 disallowUserRegistration:
                     type: boolean
                     description: disallow_user_registration disallows user registration.
diff --git a/proto/gen/store/instance_setting.pb.go b/proto/gen/store/instance_setting.pb.go
index e01305834..f4e11402a 100644
--- a/proto/gen/store/instance_setting.pb.go
+++ b/proto/gen/store/instance_setting.pb.go
@@ -313,9 +313,6 @@ func (x *InstanceBasicSetting) GetSchemaVersion() string {
 
 type InstanceGeneralSetting struct {
 	state protoimpl.MessageState `protogen:"open.v1"`
-	// theme is the name of the selected theme.
-	// This references a CSS file in the web/public/themes/ directory.
-	Theme string `protobuf:"bytes,1,opt,name=theme,proto3" json:"theme,omitempty"`
 	// disallow_user_registration disallows user registration.
 	DisallowUserRegistration bool `protobuf:"varint,2,opt,name=disallow_user_registration,json=disallowUserRegistration,proto3" json:"disallow_user_registration,omitempty"`
 	// disallow_password_auth disallows password authentication.
@@ -368,13 +365,6 @@ func (*InstanceGeneralSetting) Descriptor() ([]byte, []int) {
 	return file_store_instance_setting_proto_rawDescGZIP(), []int{2}
 }
 
-func (x *InstanceGeneralSetting) GetTheme() string {
-	if x != nil {
-		return x.Theme
-	}
-	return ""
-}
-
 func (x *InstanceGeneralSetting) GetDisallowUserRegistration() bool {
 	if x != nil {
 		return x.DisallowUserRegistration
@@ -436,7 +426,6 @@ type InstanceCustomProfile struct {
 	Title         string                 `protobuf:"bytes,1,opt,name=title,proto3" json:"title,omitempty"`
 	Description   string                 `protobuf:"bytes,2,opt,name=description,proto3" json:"description,omitempty"`
 	LogoUrl       string                 `protobuf:"bytes,3,opt,name=logo_url,json=logoUrl,proto3" json:"logo_url,omitempty"`
-	Locale        string                 `protobuf:"bytes,4,opt,name=locale,proto3" json:"locale,omitempty"`
 	unknownFields protoimpl.UnknownFields
 	sizeCache     protoimpl.SizeCache
 }
@@ -492,13 +481,6 @@ func (x *InstanceCustomProfile) GetLogoUrl() string {
 	return ""
 }
 
-func (x *InstanceCustomProfile) GetLocale() string {
-	if x != nil {
-		return x.Locale
-	}
-	return ""
-}
-
 type InstanceStorageSetting struct {
 	state protoimpl.MessageState `protogen:"open.v1"`
 	// storage_type is the storage type.
@@ -771,9 +753,8 @@ const file_store_instance_setting_proto_rawDesc = "" +
 	"\x14InstanceBasicSetting\x12\x1d\n" +
 	"\n" +
 	"secret_key\x18\x01 \x01(\tR\tsecretKey\x12%\n" +
-	"\x0eschema_version\x18\x02 \x01(\tR\rschemaVersion\"\xec\x03\n" +
-	"\x16InstanceGeneralSetting\x12\x14\n" +
-	"\x05theme\x18\x01 \x01(\tR\x05theme\x12<\n" +
+	"\x0eschema_version\x18\x02 \x01(\tR\rschemaVersion\"\xd6\x03\n" +
+	"\x16InstanceGeneralSetting\x12<\n" +
 	"\x1adisallow_user_registration\x18\x02 \x01(\bR\x18disallowUserRegistration\x124\n" +
 	"\x16disallow_password_auth\x18\x03 \x01(\bR\x14disallowPasswordAuth\x12+\n" +
 	"\x11additional_script\x18\x04 \x01(\tR\x10additionalScript\x12)\n" +
@@ -781,12 +762,11 @@ const file_store_instance_setting_proto_rawDesc = "" +
 	"\x0ecustom_profile\x18\x06 \x01(\v2\".memos.store.InstanceCustomProfileR\rcustomProfile\x121\n" +
 	"\x15week_start_day_offset\x18\a \x01(\x05R\x12weekStartDayOffset\x128\n" +
 	"\x18disallow_change_username\x18\b \x01(\bR\x16disallowChangeUsername\x128\n" +
-	"\x18disallow_change_nickname\x18\t \x01(\bR\x16disallowChangeNickname\"\x82\x01\n" +
+	"\x18disallow_change_nickname\x18\t \x01(\bR\x16disallowChangeNickname\"j\n" +
 	"\x15InstanceCustomProfile\x12\x14\n" +
 	"\x05title\x18\x01 \x01(\tR\x05title\x12 \n" +
 	"\vdescription\x18\x02 \x01(\tR\vdescription\x12\x19\n" +
-	"\blogo_url\x18\x03 \x01(\tR\alogoUrl\x12\x16\n" +
-	"\x06locale\x18\x04 \x01(\tR\x06locale\"\xd3\x02\n" +
+	"\blogo_url\x18\x03 \x01(\tR\alogoUrl\"\xd3\x02\n" +
 	"\x16InstanceStorageSetting\x12R\n" +
 	"\fstorage_type\x18\x01 \x01(\x0e2/.memos.store.InstanceStorageSetting.StorageTypeR\vstorageType\x12+\n" +
 	"\x11filepath_template\x18\x02 \x01(\tR\x10filepathTemplate\x12/\n" +
diff --git a/proto/store/instance_setting.proto b/proto/store/instance_setting.proto
index 40ffa296f..6314731c7 100644
--- a/proto/store/instance_setting.proto
+++ b/proto/store/instance_setting.proto
@@ -34,9 +34,6 @@ message InstanceBasicSetting {
 }
 
 message InstanceGeneralSetting {
-  // theme is the name of the selected theme.
-  // This references a CSS file in the web/public/themes/ directory.
-  string theme = 1;
   // disallow_user_registration disallows user registration.
   bool disallow_user_registration = 2;
   // disallow_password_auth disallows password authentication.
@@ -61,7 +58,6 @@ message InstanceCustomProfile {
   string title = 1;
   string description = 2;
   string logo_url = 3;
-  string locale = 4;
 }
 
 message InstanceStorageSetting {
diff --git a/server/router/api/v1/instance_service.go b/server/router/api/v1/instance_service.go
index 18d9461ba..cf5798499 100644
--- a/server/router/api/v1/instance_service.go
+++ b/server/router/api/v1/instance_service.go
@@ -154,14 +154,8 @@ func convertInstanceGeneralSettingFromStore(setting *storepb.InstanceGeneralSett
 	if setting == nil {
 		return nil
 	}
-	// Backfill theme if empty
-	theme := setting.Theme
-	if theme == "" {
-		theme = "default"
-	}
 
 	generalSetting := &v1pb.InstanceSetting_GeneralSetting{
-		Theme:                    theme,
 		DisallowUserRegistration: setting.DisallowUserRegistration,
 		DisallowPasswordAuth:     setting.DisallowPasswordAuth,
 		AdditionalScript:         setting.AdditionalScript,
@@ -175,7 +169,6 @@ func convertInstanceGeneralSettingFromStore(setting *storepb.InstanceGeneralSett
 			Title:       setting.CustomProfile.Title,
 			Description: setting.CustomProfile.Description,
 			LogoUrl:     setting.CustomProfile.LogoUrl,
-			Locale:      setting.CustomProfile.Locale,
 		}
 	}
 	return generalSetting
@@ -186,7 +179,6 @@ func convertInstanceGeneralSettingToStore(setting *v1pb.InstanceSetting_GeneralS
 		return nil
 	}
 	generalSetting := &storepb.InstanceGeneralSetting{
-		Theme:                    setting.Theme,
 		DisallowUserRegistration: setting.DisallowUserRegistration,
 		DisallowPasswordAuth:     setting.DisallowPasswordAuth,
 		AdditionalScript:         setting.AdditionalScript,
@@ -200,7 +192,6 @@ func convertInstanceGeneralSettingToStore(setting *v1pb.InstanceSetting_GeneralS
 			Title:       setting.CustomProfile.Title,
 			Description: setting.CustomProfile.Description,
 			LogoUrl:     setting.CustomProfile.LogoUrl,
-			Locale:      setting.CustomProfile.Locale,
 		}
 	}
 	return generalSetting
diff --git a/server/router/rss/rss.go b/server/router/rss/rss.go
index c3349a427..a21a59c07 100644
--- a/server/router/rss/rss.go
+++ b/server/router/rss/rss.go
@@ -415,15 +415,9 @@ func getRSSHeading(ctx context.Context, stores *store.Store) (RSSHeading, error)
 	}
 	customProfile := settings.CustomProfile
 
-	// Use locale as language if available, default to en-us
-	language := "en-us"
-	if customProfile.Locale != "" {
-		language = customProfile.Locale
-	}
-
 	return RSSHeading{
 		Title:       customProfile.Title,
 		Description: customProfile.Description,
-		Language:    language,
+		Language:    "en-us",
 	}, nil
 }
diff --git a/web/src/App.tsx b/web/src/App.tsx
index df13766ce..58b7179a4 100644
--- a/web/src/App.tsx
+++ b/web/src/App.tsx
@@ -5,7 +5,7 @@ import { Outlet } from "react-router-dom";
 import useNavigateTo from "./hooks/useNavigateTo";
 import { instanceStore, userStore } from "./store";
 import { cleanupExpiredOAuthState } from "./utils/oauth";
-import { loadTheme, setupSystemThemeListener } from "./utils/theme";
+import { getThemeWithFallback, loadTheme, setupSystemThemeListener } from "./utils/theme";
 
 const App = observer(() => {
   const { i18n } = useTranslation();
@@ -54,55 +54,44 @@ const App = observer(() => {
     link.href = instanceGeneralSetting.customProfile.logoUrl || "/logo.webp";
   }, [instanceGeneralSetting.customProfile]);
 
+  // Update HTML lang and dir attributes based on current locale
   useEffect(() => {
-    const currentLocale = instanceStore.state.locale;
-    // This will trigger re-rendering of the whole app.
-    i18n.changeLanguage(currentLocale);
+    const currentLocale = i18n.language;
     document.documentElement.setAttribute("lang", currentLocale);
     if (["ar", "fa"].includes(currentLocale)) {
       document.documentElement.setAttribute("dir", "rtl");
     } else {
       document.documentElement.setAttribute("dir", "ltr");
     }
-  }, [instanceStore.state.locale]);
+  }, [i18n.language]);
 
+  // Apply theme when user setting changes
   useEffect(() => {
     if (!userGeneralSetting) {
       return;
     }
-
-    instanceStore.state.setPartial({
-      locale: userGeneralSetting.locale || instanceStore.state.locale,
-      theme: userGeneralSetting.theme || instanceStore.state.theme,
-    });
-  }, [userGeneralSetting?.locale, userGeneralSetting?.theme]);
-
-  // Load theme when instance theme changes or user setting changes
-  useEffect(() => {
-    const currentTheme = userGeneralSetting?.theme || instanceStore.state.theme;
-    if (currentTheme) {
-      loadTheme(currentTheme);
-    }
-  }, [userGeneralSetting?.theme, instanceStore.state.theme]);
+    const theme = getThemeWithFallback(userGeneralSetting.theme);
+    loadTheme(theme);
+  }, [userGeneralSetting?.theme]);
 
   // Listen for system theme changes when using "system" theme
   useEffect(() => {
-    const currentTheme = userGeneralSetting?.theme || instanceStore.state.theme;
+    const theme = getThemeWithFallback(userGeneralSetting?.theme);
 
     // Only set up listener if theme is "system"
-    if (currentTheme !== "system") {
+    if (theme !== "system") {
       return;
     }
 
     // Set up listener for OS theme preference changes
     const cleanup = setupSystemThemeListener(() => {
       // Reload theme when system preference changes
-      loadTheme(currentTheme);
+      loadTheme(theme);
     });
 
     // Cleanup listener on unmount or when theme changes
     return cleanup;
-  }, [userGeneralSetting?.theme, instanceStore.state.theme]);
+  }, [userGeneralSetting?.theme]);
 
   return <Outlet />;
 });
diff --git a/web/src/components/AuthFooter.tsx b/web/src/components/AuthFooter.tsx
index a4d36cad0..f68f05ed0 100644
--- a/web/src/components/AuthFooter.tsx
+++ b/web/src/components/AuthFooter.tsx
@@ -1,6 +1,8 @@
 import { observer } from "mobx-react-lite";
+import { useTranslation } from "react-i18next";
+import i18n from "@/i18n";
 import { cn } from "@/lib/utils";
-import { instanceStore } from "@/store";
+import { getInitialTheme, loadTheme } from "@/utils/theme";
 import LocaleSelect from "./LocaleSelect";
 import ThemeSelect from "./ThemeSelect";
 
@@ -9,10 +11,22 @@ interface Props {
 }
 
 const AuthFooter = observer(({ className }: Props) => {
+  const { i18n: i18nInstance } = useTranslation();
+  const currentLocale = i18nInstance.language as Locale;
+  const currentTheme = getInitialTheme();
+
+  const handleLocaleChange = (locale: Locale) => {
+    i18n.changeLanguage(locale);
+  };
+
+  const handleThemeChange = (theme: string) => {
+    loadTheme(theme);
+  };
+
   return (
     <div className={cn("mt-4 flex flex-row items-center justify-center w-full gap-2", className)}>
-      <LocaleSelect value={instanceStore.state.locale} onChange={(locale) => instanceStore.state.setPartial({ locale })} />
-      <ThemeSelect value={instanceStore.state.theme} onValueChange={(theme) => instanceStore.state.setPartial({ theme })} />
+      <LocaleSelect value={currentLocale} onChange={handleLocaleChange} />
+      <ThemeSelect value={currentTheme} onValueChange={handleThemeChange} />
     </div>
   );
 });
diff --git a/web/src/components/MemoContent/CodeBlock.tsx b/web/src/components/MemoContent/CodeBlock.tsx
index 6ab45b006..b6a6dcce2 100644
--- a/web/src/components/MemoContent/CodeBlock.tsx
+++ b/web/src/components/MemoContent/CodeBlock.tsx
@@ -4,7 +4,8 @@ import { CheckIcon, CopyIcon } from "lucide-react";
 import { observer } from "mobx-react-lite";
 import { useEffect, useMemo, useState } from "react";
 import { cn } from "@/lib/utils";
-import { instanceStore } from "@/store";
+import { userStore } from "@/store";
+import { getThemeWithFallback, resolveTheme } from "@/utils/theme";
 import { MermaidBlock } from "./MermaidBlock";
 
 interface PreProps {
@@ -93,8 +94,9 @@ export const CodeBlock = observer(({ children, className, ...props }: PreProps)
     );
   }
 
-  const appTheme = instanceStore.state.theme;
-  const isDarkTheme = appTheme.includes("dark");
+  const theme = getThemeWithFallback(userStore.state.userGeneralSetting?.theme);
+  const resolvedTheme = resolveTheme(theme);
+  const isDarkTheme = resolvedTheme.includes("dark");
 
   // Dynamically load highlight.js theme based on app theme
   useEffect(() => {
@@ -121,7 +123,7 @@ export const CodeBlock = observer(({ children, className, ...props }: PreProps)
     };
 
     dynamicImportStyle();
-  }, [appTheme, isDarkTheme]);
+  }, [resolvedTheme, isDarkTheme]);
 
   // Highlight code using highlight.js
   const highlightedCode = useMemo(() => {
diff --git a/web/src/components/MemoContent/MermaidBlock.tsx b/web/src/components/MemoContent/MermaidBlock.tsx
index f28978c92..951ba08ad 100644
--- a/web/src/components/MemoContent/MermaidBlock.tsx
+++ b/web/src/components/MemoContent/MermaidBlock.tsx
@@ -2,8 +2,8 @@ import mermaid from "mermaid";
 import { observer } from "mobx-react-lite";
 import { useEffect, useMemo, useRef, useState } from "react";
 import { cn } from "@/lib/utils";
-import { instanceStore, userStore } from "@/store";
-import { resolveTheme, setupSystemThemeListener } from "@/utils/theme";
+import { userStore } from "@/store";
+import { getThemeWithFallback, resolveTheme, setupSystemThemeListener } from "@/utils/theme";
 
 interface MermaidBlockProps {
   children?: React.ReactNode;
@@ -25,7 +25,8 @@ export const MermaidBlock = observer(({ children, className }: MermaidBlockProps
   const codeContent = String(codeElement?.props?.children || "").replace(/\n$/, "");
 
   // Get theme preference (reactive via MobX observer)
-  const themePreference = userStore.state.userGeneralSetting?.theme || instanceStore.state.theme;
+  // Falls back to localStorage or system preference if no user setting
+  const themePreference = getThemeWithFallback(userStore.state.userGeneralSetting?.theme);
 
   // Resolve theme to actual value (handles "system" theme + system theme changes)
   const currentTheme = useMemo(() => resolveTheme(themePreference), [themePreference, systemThemeChange]);
diff --git a/web/src/components/Settings/InstanceSection.tsx b/web/src/components/Settings/InstanceSection.tsx
index 30512541d..e0e2203aa 100644
--- a/web/src/components/Settings/InstanceSection.tsx
+++ b/web/src/components/Settings/InstanceSection.tsx
@@ -13,7 +13,6 @@ import { instanceSettingNamePrefix } from "@/store/common";
 import { IdentityProvider } from "@/types/proto/api/v1/idp_service";
 import { InstanceSetting_GeneralSetting, InstanceSetting_Key } from "@/types/proto/api/v1/instance_service";
 import { useTranslate } from "@/utils/i18n";
-import ThemeSelect from "../ThemeSelect";
 import UpdateCustomizedProfileDialog from "../UpdateCustomizedProfileDialog";
 import SettingGroup from "./SettingGroup";
 import SettingRow from "./SettingRow";
@@ -79,14 +78,6 @@ const InstanceSection = observer(() => {
       </SettingGroup>
 
       <SettingGroup title={t("setting.system-section.title")} showSeparator>
-        <SettingRow label="Theme">
-          <ThemeSelect
-            value={instanceGeneralSetting.theme || "default"}
-            onValueChange={(value: string) => updatePartialSetting({ theme: value })}
-            className="min-w-fit"
-          />
-        </SettingRow>
-
         <SettingRow label={t("setting.system-section.additional-style")} vertical>
           <Textarea
             className="font-mono w-full"
diff --git a/web/src/components/Settings/PreferencesSection.tsx b/web/src/components/Settings/PreferencesSection.tsx
index 70110b817..78326e274 100644
--- a/web/src/components/Settings/PreferencesSection.tsx
+++ b/web/src/components/Settings/PreferencesSection.tsx
@@ -1,10 +1,12 @@
 import { observer } from "mobx-react-lite";
 import { Select, SelectContent, SelectItem, SelectTrigger, SelectValue } from "@/components/ui/select";
-import { instanceStore, userStore } from "@/store";
+import i18n from "@/i18n";
+import { userStore } from "@/store";
 import { Visibility } from "@/types/proto/api/v1/memo_service";
 import { UserSetting_GeneralSetting } from "@/types/proto/api/v1/user_service";
 import { useTranslate } from "@/utils/i18n";
 import { convertVisibilityFromString, convertVisibilityToString } from "@/utils/memo";
+import { loadTheme } from "@/utils/theme";
 import LocaleSelect from "../LocaleSelect";
 import ThemeSelect from "../ThemeSelect";
 import VisibilityIcon from "../VisibilityIcon";
@@ -18,8 +20,8 @@ const PreferencesSection = observer(() => {
   const generalSetting = userStore.state.userGeneralSetting;
 
   const handleLocaleSelectChange = async (locale: Locale) => {
-    // Update instance store immediately for instant UI feedback
-    instanceStore.state.setPartial({ locale });
+    // Apply locale immediately for instant UI feedback
+    i18n.changeLanguage(locale);
     // Persist to user settings
     await userStore.updateUserGeneralSetting({ locale }, ["locale"]);
   };
@@ -29,8 +31,8 @@ const PreferencesSection = observer(() => {
   };
 
   const handleThemeChange = async (theme: string) => {
-    // Update instance store immediately for instant UI feedback
-    instanceStore.state.setPartial({ theme });
+    // Apply theme immediately for instant UI feedback
+    loadTheme(theme);
     // Persist to user settings
     await userStore.updateUserGeneralSetting({ theme }, ["theme"]);
   };
diff --git a/web/src/components/ThemeSelect.tsx b/web/src/components/ThemeSelect.tsx
index 5668461b8..af045b6a7 100644
--- a/web/src/components/ThemeSelect.tsx
+++ b/web/src/components/ThemeSelect.tsx
@@ -1,6 +1,5 @@
 import { Monitor, Moon, MoonStar, Palette, Sun, Wallpaper } from "lucide-react";
 import { Select, SelectContent, SelectItem, SelectTrigger, SelectValue } from "@/components/ui/select";
-import { instanceStore } from "@/store";
 import { THEME_OPTIONS } from "@/utils/theme";
 
 interface ThemeSelectProps {
@@ -19,13 +18,11 @@ const THEME_ICONS: Record<string, JSX.Element> = {
 };
 
 const ThemeSelect = ({ value, onValueChange, className }: ThemeSelectProps = {}) => {
-  const currentTheme = value || instanceStore.state.theme || "system";
+  const currentTheme = value || "system";
 
-  const handleThemeChange = (newTheme: Theme) => {
+  const handleThemeChange = (newTheme: string) => {
     if (onValueChange) {
       onValueChange(newTheme);
-    } else {
-      instanceStore.setTheme(newTheme);
     }
   };
 
diff --git a/web/src/components/UpdateCustomizedProfileDialog.tsx b/web/src/components/UpdateCustomizedProfileDialog.tsx
index 1275d1b8f..d390ff3b3 100644
--- a/web/src/components/UpdateCustomizedProfileDialog.tsx
+++ b/web/src/components/UpdateCustomizedProfileDialog.tsx
@@ -9,8 +9,6 @@ import { instanceStore } from "@/store";
 import { instanceSettingNamePrefix } from "@/store/common";
 import { InstanceSetting_GeneralSetting_CustomProfile, InstanceSetting_Key } from "@/types/proto/api/v1/instance_service";
 import { useTranslate } from "@/utils/i18n";
-import LocaleSelect from "./LocaleSelect";
-import ThemeSelect from "./ThemeSelect";
 
 interface Props {
   open: boolean;
@@ -52,18 +50,11 @@ function UpdateCustomizedProfileDialog({ open, onOpenChange, onSuccess }: Props)
     });
   };
 
-  const handleLocaleSelectChange = (locale: Locale) => {
-    setPartialState({
-      locale: locale,
-    });
-  };
-
   const handleRestoreButtonClick = () => {
     setPartialState({
       title: "Memos",
       logoUrl: "/logo.webp",
       description: "",
-      locale: "en",
     });
   };
 
@@ -126,16 +117,6 @@ function UpdateCustomizedProfileDialog({ open, onOpenChange, onSuccess }: Props)
               placeholder="Enter description"
             />
           </div>
-
-          <div className="grid gap-2">
-            <Label>{t("setting.system-section.customize-server.locale")}</Label>
-            <LocaleSelect value={customProfile.locale} onChange={handleLocaleSelectChange} />
-          </div>
-
-          <div className="grid gap-2">
-            <Label>Theme</Label>
-            <ThemeSelect />
-          </div>
         </div>
 
         <DialogFooter className="flex-col sm:flex-row sm:justify-between gap-2">
diff --git a/web/src/components/UserMenu.tsx b/web/src/components/UserMenu.tsx
index a86b9fc1f..f359c22cd 100644
--- a/web/src/components/UserMenu.tsx
+++ b/web/src/components/UserMenu.tsx
@@ -3,12 +3,12 @@ import { observer } from "mobx-react-lite";
 import { authServiceClient } from "@/grpcweb";
 import useCurrentUser from "@/hooks/useCurrentUser";
 import useNavigateTo from "@/hooks/useNavigateTo";
-import { locales } from "@/i18n";
+import i18n, { locales } from "@/i18n";
 import { cn } from "@/lib/utils";
 import { Routes } from "@/router";
-import { instanceStore, userStore } from "@/store";
+import { userStore } from "@/store";
 import { getLocaleDisplayName, useTranslate } from "@/utils/i18n";
-import { THEME_OPTIONS } from "@/utils/theme";
+import { loadTheme, THEME_OPTIONS } from "@/utils/theme";
 import UserAvatar from "./UserAvatar";
 import {
   DropdownMenu,
@@ -34,13 +34,16 @@ const UserMenu = observer((props: Props) => {
   const currentTheme = generalSetting?.theme || "default";
 
   const handleLocaleChange = async (locale: Locale) => {
-    // Update instance store immediately for instant UI feedback
-    instanceStore.state.setPartial({ locale });
+    // Apply locale immediately for instant UI feedback
+    i18n.changeLanguage(locale);
     // Persist to user settings
     await userStore.updateUserGeneralSetting({ locale }, ["locale"]);
   };
 
   const handleThemeChange = async (theme: string) => {
+    // Apply theme immediately for instant UI feedback
+    loadTheme(theme);
+    // Persist to user settings
     await userStore.updateUserGeneralSetting({ theme }, ["theme"]);
   };
 
diff --git a/web/src/main.tsx b/web/src/main.tsx
index cd747a044..782769c93 100644
--- a/web/src/main.tsx
+++ b/web/src/main.tsx
@@ -9,11 +9,12 @@ import router from "./router";
 // Configure MobX before importing any stores
 import "./store/config";
 import { initialInstanceStore } from "./store/instance";
-import { initialUserStore } from "./store/user";
+import userStore, { initialUserStore } from "./store/user";
 import { applyThemeEarly } from "./utils/theme";
 import "leaflet/dist/leaflet.css";
 
 // Apply theme early to prevent flash of wrong theme
+// This uses localStorage as the source before user settings are loaded
 applyThemeEarly();
 
 const Main = observer(() => (
@@ -24,9 +25,14 @@ const Main = observer(() => (
 ));
 
 (async () => {
+  // Initialize stores
   await initialInstanceStore();
   await initialUserStore();
 
+  // Apply user preferences (theme & locale) after user settings are loaded
+  // This will override the early theme with user's actual preference
+  userStore.applyUserPreferences();
+
   const container = document.getElementById("root");
   const root = createRoot(container as HTMLElement);
   root.render(<Main />);
diff --git a/web/src/store/index.ts b/web/src/store/index.ts
index 03ef04013..25b57b6ee 100644
--- a/web/src/store/index.ts
+++ b/web/src/store/index.ts
@@ -22,9 +22,6 @@ export {
   memoNamePrefix,
   userNamePrefix,
 } from "./common";
-// Re-export instance types
-export type { Theme } from "./instance";
-export { isValidTheme } from "./instance";
 // Re-export filter types
 export type { FilterFactor, MemoFilter } from "./memoFilter";
 export { getMemoFilterKey, parseFilterQuery, stringifyFilters } from "./memoFilter";
diff --git a/web/src/store/instance.ts b/web/src/store/instance.ts
index 19f896832..68900b832 100644
--- a/web/src/store/instance.ts
+++ b/web/src/store/instance.ts
@@ -9,21 +9,11 @@ import {
   InstanceSetting_Key,
   InstanceSetting_MemoRelatedSetting,
 } from "@/types/proto/api/v1/instance_service";
-import { isValidateLocale } from "@/utils/i18n";
 import { createServerStore, StandardState } from "./base-store";
 import { instanceSettingNamePrefix } from "./common";
 import { createRequestKey } from "./store-utils";
 
-const VALID_THEMES = ["system", "default", "default-dark", "midnight", "paper", "whitewall"] as const;
-export type Theme = (typeof VALID_THEMES)[number];
-
-export function isValidTheme(theme: string): theme is Theme {
-  return VALID_THEMES.includes(theme as Theme);
-}
-
 class InstanceState extends StandardState {
-  locale: string = "en";
-  theme: Theme | string = "system";
   profile: InstanceProfile = InstanceProfile.fromPartial({});
   settings: InstanceSetting[] = [];
 
@@ -42,29 +32,6 @@ class InstanceState extends StandardState {
       return setting?.memoRelatedSetting || InstanceSetting_MemoRelatedSetting.fromPartial({});
     }).get();
   }
-
-  setPartial(partial: Partial<InstanceState>): void {
-    const finalState = { ...this, ...partial };
-
-    // Validate locale
-    if (partial.locale !== undefined && !isValidateLocale(finalState.locale)) {
-      console.warn(`Invalid locale "${finalState.locale}", falling back to "en"`);
-      finalState.locale = "en";
-    }
-
-    // Validate theme - accept string and validate
-    if (partial.theme !== undefined) {
-      const themeStr = String(finalState.theme);
-      if (!isValidTheme(themeStr)) {
-        console.warn(`Invalid theme "${themeStr}", falling back to "default"`);
-        finalState.theme = "default";
-      } else {
-        finalState.theme = themeStr;
-      }
-    }
-
-    Object.assign(this, finalState);
-  }
 }
 
 const instanceStore = (() => {
@@ -114,33 +81,6 @@ const instanceStore = (() => {
     return setting || InstanceSetting.fromPartial({});
   };
 
-  const setTheme = async (theme: string): Promise<void> => {
-    // Validate theme
-    if (!isValidTheme(theme)) {
-      console.warn(`Invalid theme "${theme}", ignoring`);
-      return;
-    }
-
-    // Update local state immediately
-    state.setPartial({ theme });
-
-    // Persist to server
-    const generalSetting = state.generalSetting;
-    const updatedGeneralSetting = InstanceSetting_GeneralSetting.fromPartial({
-      ...generalSetting,
-      customProfile: {
-        ...generalSetting.customProfile,
-      },
-    });
-
-    await upsertInstanceSetting(
-      InstanceSetting.fromPartial({
-        name: `${instanceSettingNamePrefix}${InstanceSetting_Key.GENERAL}`,
-        generalSetting: updatedGeneralSetting,
-      }),
-    );
-  };
-
   const fetchInstanceProfile = async (): Promise<InstanceProfile> => {
     const requestKey = createRequestKey("fetchInstanceProfile");
 
@@ -161,7 +101,6 @@ const instanceStore = (() => {
     fetchInstanceProfile,
     upsertInstanceSetting,
     getInstanceSettingByKey,
-    setTheme,
   };
 })();
 
@@ -178,19 +117,9 @@ export const initialInstanceStore = async (): Promise<void> => {
     ]);
 
     // Apply settings to state
-    const instanceGeneralSetting = instanceStore.state.generalSetting;
-    instanceStore.state.setPartial({
-      locale: instanceGeneralSetting.customProfile?.locale || "en",
-      theme: instanceGeneralSetting.theme || "system",
-      profile: instanceProfile,
-    });
+    Object.assign(instanceStore.state, { profile: instanceProfile });
   } catch (error) {
     console.error("Failed to initialize instance store:", error);
-    // Set default fallback values
-    instanceStore.state.setPartial({
-      locale: "en",
-      theme: "system",
-    });
   }
 };
 
diff --git a/web/src/store/user.ts b/web/src/store/user.ts
index d86bf173b..88f93fd5b 100644
--- a/web/src/store/user.ts
+++ b/web/src/store/user.ts
@@ -1,6 +1,7 @@
 import { uniqueId } from "lodash-es";
 import { computed, makeAutoObservable } from "mobx";
 import { authServiceClient, shortcutServiceClient, userServiceClient } from "@/grpcweb";
+import i18n from "@/i18n";
 import { Shortcut } from "@/types/proto/api/v1/shortcut_service";
 import {
   User,
@@ -13,8 +14,8 @@ import {
   UserSetting_WebhooksSetting,
   UserStats,
 } from "@/types/proto/api/v1/user_service";
-import { findNearestMatchedLanguage } from "@/utils/i18n";
-import instanceStore from "./instance";
+import { getLocaleWithFallback } from "@/utils/i18n";
+import { getThemeWithFallback, loadTheme } from "@/utils/theme";
 import { createRequestKey, RequestDeduplicator, StoreError } from "./store-utils";
 
 class LocalState {
@@ -283,6 +284,20 @@ const userStore = (() => {
     state.statsStateId = id;
   };
 
+  // Applies user preferences (theme and locale) with proper fallbacks
+  // This should be called after user settings are loaded
+  const applyUserPreferences = () => {
+    const generalSetting = state.userGeneralSetting;
+
+    // Apply theme with fallback: user setting -> localStorage -> system
+    const theme = getThemeWithFallback(generalSetting?.theme);
+    loadTheme(theme);
+
+    // Apply locale with fallback: user setting -> browser language
+    const locale = getLocaleWithFallback(generalSetting?.locale);
+    i18n.changeLanguage(locale);
+  };
+
   return {
     state,
     getOrFetchUserByName,
@@ -299,6 +314,7 @@ const userStore = (() => {
     deleteNotification,
     fetchUserStats,
     setStatsStateId,
+    applyUserPreferences,
   };
 })();
 
@@ -306,22 +322,18 @@ const userStore = (() => {
 // 1. Fetch current authenticated user session
 // 2. Set current user in store (required for subsequent calls)
 // 3. Fetch user settings (depends on currentUser being set)
-// 4. Apply user preferences to instance store
 export const initialUserStore = async () => {
   try {
     // Step 1: Authenticate and get current user
     const { user: currentUser } = await authServiceClient.getCurrentSession({});
 
     if (!currentUser) {
-      // No authenticated user - clear state and use default locale
+      // No authenticated user - clear state
       userStore.state.setPartial({
         currentUser: undefined,
         userGeneralSetting: undefined,
         userMapByName: {},
       });
-
-      const locale = findNearestMatchedLanguage(navigator.language);
-      instanceStore.state.setPartial({ locale });
       return;
     }
 
@@ -339,27 +351,8 @@ export const initialUserStore = async () => {
     // CRITICAL: This must happen after currentUser is set in step 2
     // The fetchUserSettings() and fetchUserStats() methods check state.currentUser internally
     await Promise.all([userStore.fetchUserSettings(), userStore.fetchUserStats()]);
-
-    // Step 4: Apply user preferences to instance
-    // CRITICAL: This must happen after fetchUserSettings() completes
-    // We need userGeneralSetting to be populated before accessing it
-    const generalSetting = userStore.state.userGeneralSetting;
-    if (generalSetting) {
-      // Note: setPartial will validate theme automatically
-      instanceStore.state.setPartial({
-        locale: generalSetting.locale,
-        theme: generalSetting.theme || "default", // Validation handled by setPartial
-      });
-    } else {
-      // Fallback if settings weren't loaded
-      const locale = findNearestMatchedLanguage(navigator.language);
-      instanceStore.state.setPartial({ locale });
-    }
   } catch (error) {
-    // On any error, fall back to browser language detection
     console.error("Failed to initialize user store:", error);
-    const locale = findNearestMatchedLanguage(navigator.language);
-    instanceStore.state.setPartial({ locale });
   }
 };
 
diff --git a/web/src/types/proto/api/v1/instance_service.ts b/web/src/types/proto/api/v1/instance_service.ts
index e4b356613..73fb72eac 100644
--- a/web/src/types/proto/api/v1/instance_service.ts
+++ b/web/src/types/proto/api/v1/instance_service.ts
@@ -92,11 +92,6 @@ export function instanceSetting_KeyToNumber(object: InstanceSetting_Key): number
 
 /** General instance settings configuration. */
 export interface InstanceSetting_GeneralSetting {
-  /**
-   * theme is the name of the selected theme.
-   * This references a CSS file in the web/public/themes/ directory.
-   */
-  theme: string;
   /** disallow_user_registration disallows user registration. */
   disallowUserRegistration: boolean;
   /** disallow_password_auth disallows password authentication. */
@@ -126,7 +121,6 @@ export interface InstanceSetting_GeneralSetting_CustomProfile {
   title: string;
   description: string;
   logoUrl: string;
-  locale: string;
 }
 
 /** Storage configuration settings for instance attachments. */
@@ -453,7 +447,6 @@ export const InstanceSetting: MessageFns<InstanceSetting> = {
 
 function createBaseInstanceSetting_GeneralSetting(): InstanceSetting_GeneralSetting {
   return {
-    theme: "",
     disallowUserRegistration: false,
     disallowPasswordAuth: false,
     additionalScript: "",
@@ -467,9 +460,6 @@ function createBaseInstanceSetting_GeneralSetting(): InstanceSetting_GeneralSett
 
 export const InstanceSetting_GeneralSetting: MessageFns<InstanceSetting_GeneralSetting> = {
   encode(message: InstanceSetting_GeneralSetting, writer: BinaryWriter = new BinaryWriter()): BinaryWriter {
-    if (message.theme !== "") {
-      writer.uint32(10).string(message.theme);
-    }
     if (message.disallowUserRegistration !== false) {
       writer.uint32(16).bool(message.disallowUserRegistration);
     }
@@ -504,14 +494,6 @@ export const InstanceSetting_GeneralSetting: MessageFns<InstanceSetting_GeneralS
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
-        case 1: {
-          if (tag !== 10) {
-            break;
-          }
-
-          message.theme = reader.string();
-          continue;
-        }
         case 2: {
           if (tag !== 16) {
             break;
@@ -590,7 +572,6 @@ export const InstanceSetting_GeneralSetting: MessageFns<InstanceSetting_GeneralS
   },
   fromPartial(object: DeepPartial<InstanceSetting_GeneralSetting>): InstanceSetting_GeneralSetting {
     const message = createBaseInstanceSetting_GeneralSetting();
-    message.theme = object.theme ?? "";
     message.disallowUserRegistration = object.disallowUserRegistration ?? false;
     message.disallowPasswordAuth = object.disallowPasswordAuth ?? false;
     message.additionalScript = object.additionalScript ?? "";
@@ -606,7 +587,7 @@ export const InstanceSetting_GeneralSetting: MessageFns<InstanceSetting_GeneralS
 };
 
 function createBaseInstanceSetting_GeneralSetting_CustomProfile(): InstanceSetting_GeneralSetting_CustomProfile {
-  return { title: "", description: "", logoUrl: "", locale: "" };
+  return { title: "", description: "", logoUrl: "" };
 }
 
 export const InstanceSetting_GeneralSetting_CustomProfile: MessageFns<InstanceSetting_GeneralSetting_CustomProfile> = {
@@ -623,9 +604,6 @@ export const InstanceSetting_GeneralSetting_CustomProfile: MessageFns<InstanceSe
     if (message.logoUrl !== "") {
       writer.uint32(26).string(message.logoUrl);
     }
-    if (message.locale !== "") {
-      writer.uint32(34).string(message.locale);
-    }
     return writer;
   },
 
@@ -660,14 +638,6 @@ export const InstanceSetting_GeneralSetting_CustomProfile: MessageFns<InstanceSe
           message.logoUrl = reader.string();
           continue;
         }
-        case 4: {
-          if (tag !== 34) {
-            break;
-          }
-
-          message.locale = reader.string();
-          continue;
-        }
       }
       if ((tag & 7) === 4 || tag === 0) {
         break;
@@ -689,7 +659,6 @@ export const InstanceSetting_GeneralSetting_CustomProfile: MessageFns<InstanceSe
     message.title = object.title ?? "";
     message.description = object.description ?? "";
     message.logoUrl = object.logoUrl ?? "";
-    message.locale = object.locale ?? "";
     return message;
   },
 };
diff --git a/web/src/utils/i18n.ts b/web/src/utils/i18n.ts
index fc4e2f9e1..c50a174be 100644
--- a/web/src/utils/i18n.ts
+++ b/web/src/utils/i18n.ts
@@ -52,6 +52,19 @@ export const isValidateLocale = (locale: string | undefined | null): boolean =>
   return locales.includes(locale);
 };
 
+// Gets the locale to use with proper priority:
+// 1. User setting (if logged in and has preference)
+// 2. Browser language preference
+export const getLocaleWithFallback = (userLocale?: string): Locale => {
+  // Priority 1: User setting (if logged in and valid)
+  if (userLocale && isValidateLocale(userLocale)) {
+    return userLocale as Locale;
+  }
+
+  // Priority 2: Browser language
+  return findNearestMatchedLanguage(navigator.language);
+};
+
 // Get the display name for a locale in its native language
 export const getLocaleDisplayName = (locale: string): string => {
   try {
diff --git a/web/src/utils/theme.ts b/web/src/utils/theme.ts
index ee61b77cc..4b10bec68 100644
--- a/web/src/utils/theme.ts
+++ b/web/src/utils/theme.ts
@@ -3,11 +3,24 @@ import midnightThemeContent from "../themes/midnight.css?raw";
 import paperThemeContent from "../themes/paper.css?raw";
 import whitewallThemeContent from "../themes/whitewall.css?raw";
 
-const VALID_THEMES = ["system", "default", "default-dark", "midnight", "paper", "whitewall"] as const;
-type ValidTheme = (typeof VALID_THEMES)[number];
+// ============================================================================
+// Types and Constants
+// ============================================================================
 
-const THEME_CONTENT: Record<ValidTheme, string | null> = {
-  system: null, // System theme dynamically chooses between default and default-dark
+const VALID_THEMES = ["system", "default", "default-dark", "midnight", "paper", "whitewall"] as const;
+
+export type Theme = (typeof VALID_THEMES)[number];
+export type ResolvedTheme = Exclude<Theme, "system">;
+
+export interface ThemeOption {
+  value: string;
+  label: string;
+}
+
+const STORAGE_KEY = "memos-theme";
+const STYLE_ELEMENT_ID = "instance-theme";
+
+const THEME_CONTENT: Record<ResolvedTheme, string | null> = {
   default: null,
   "default-dark": defaultDarkThemeContent,
   midnight: midnightThemeContent,
@@ -15,11 +28,6 @@ const THEME_CONTENT: Record<ValidTheme, string | null> = {
   whitewall: whitewallThemeContent,
 };
 
-export interface ThemeOption {
-  value: string;
-  label: string;
-}
-
 export const THEME_OPTIONS: ThemeOption[] = [
   { value: "system", label: "Sync with system" },
   { value: "default", label: "Light" },
@@ -29,102 +37,201 @@ export const THEME_OPTIONS: ThemeOption[] = [
   { value: "whitewall", label: "Whitewall" },
 ];
 
-const validateTheme = (theme: string): ValidTheme => {
-  return VALID_THEMES.includes(theme as ValidTheme) ? (theme as ValidTheme) : "default";
+// ============================================================================
+// Theme Validation and Detection
+// ============================================================================
+
+/**
+ * Validates and normalizes a theme string to a valid theme.
+ * Falls back to "default" for invalid themes.
+ */
+const validateTheme = (theme: string): Theme => {
+  return VALID_THEMES.includes(theme as Theme) ? (theme as Theme) : "default";
 };
 
-export const getSystemTheme = (): "default" | "default-dark" => {
-  if (typeof window !== "undefined" && window.matchMedia) {
-    return window.matchMedia("(prefers-color-scheme: dark)").matches ? "default-dark" : "default";
+/**
+ * Detects the system's preferred color scheme.
+ * @returns "default-dark" for dark mode, "default" for light mode
+ */
+export const getSystemTheme = (): ResolvedTheme => {
+  if (typeof window !== "undefined" && window.matchMedia?.("(prefers-color-scheme: dark)").matches) {
+    return "default-dark";
   }
   return "default";
 };
 
-// Resolves "system" to actual theme based on OS preference
-export const resolveTheme = (theme: string): "default" | "default-dark" | "midnight" | "paper" | "whitewall" => {
-  if (theme === "system") {
-    return getSystemTheme();
-  }
+/**
+ * Resolves "system" theme to the actual theme based on OS preference.
+ * Other themes are returned as-is after validation.
+ */
+export const resolveTheme = (theme: string): ResolvedTheme => {
   const validTheme = validateTheme(theme);
   return validTheme === "system" ? getSystemTheme() : validTheme;
 };
 
-// Gets the theme that should be applied on initial load
-export const getInitialTheme = (): ValidTheme => {
-  // Try to get stored theme from localStorage
+// ============================================================================
+// LocalStorage Helpers
+// ============================================================================
+
+/**
+ * Safely reads the theme from localStorage.
+ * @returns The stored theme, or null if not found or unavailable
+ */
+const getStoredTheme = (): Theme | null => {
   try {
-    const storedTheme = localStorage.getItem("memos-theme");
-    if (storedTheme && VALID_THEMES.includes(storedTheme as ValidTheme)) {
-      return storedTheme as ValidTheme;
-    }
+    const stored = localStorage.getItem(STORAGE_KEY);
+    return stored && VALID_THEMES.includes(stored as Theme) ? (stored as Theme) : null;
   } catch {
-    // localStorage might not be available
+    return null;
+  }
+};
+
+/**
+ * Safely stores the theme to localStorage.
+ */
+const setStoredTheme = (theme: Theme): void => {
+  try {
+    localStorage.setItem(STORAGE_KEY, theme);
+  } catch {
+    // localStorage might not be available (SSR, private browsing, etc.)
+  }
+};
+
+// ============================================================================
+// Theme Selection with Fallbacks
+// ============================================================================
+
+/**
+ * Gets the theme for initial page load (before user settings are available).
+ * Priority: localStorage -> system preference
+ */
+export const getInitialTheme = (): Theme => {
+  return getStoredTheme() ?? "system";
+};
+
+/**
+ * Gets the theme with full fallback chain.
+ * Priority:
+ * 1. User setting (if logged in and has preference)
+ * 2. localStorage (from previous session)
+ * 3. System preference
+ */
+export const getThemeWithFallback = (userTheme?: string): Theme => {
+  // Priority 1: User setting
+  if (userTheme && VALID_THEMES.includes(userTheme as Theme)) {
+    return userTheme as Theme;
   }
 
+  // Priority 2: localStorage
+  const stored = getStoredTheme();
+  if (stored) {
+    return stored;
+  }
+
+  // Priority 3: System preference
   return "system";
 };
 
-// Applies the theme early to prevent flash of wrong theme
+// ============================================================================
+// DOM Manipulation
+// ============================================================================
+
+/**
+ * Removes the existing theme style element from the DOM.
+ */
+const removeThemeStyle = (): void => {
+  document.getElementById(STYLE_ELEMENT_ID)?.remove();
+};
+
+/**
+ * Injects theme CSS into the document head.
+ * Skips injection for the default theme (uses base CSS).
+ */
+const injectThemeStyle = (theme: ResolvedTheme): void => {
+  removeThemeStyle();
+
+  if (theme === "default") {
+    return; // Use base CSS for default theme
+  }
+
+  const css = THEME_CONTENT[theme];
+  if (css) {
+    const style = document.createElement("style");
+    style.id = STYLE_ELEMENT_ID;
+    style.textContent = css;
+    document.head.appendChild(style);
+  }
+};
+
+/**
+ * Sets the data-theme attribute on the document element.
+ * This allows CSS to react to the current theme.
+ */
+const setThemeAttribute = (theme: ResolvedTheme): void => {
+  document.documentElement.setAttribute("data-theme", theme);
+};
+
+// ============================================================================
+// Main Theme Loading
+// ============================================================================
+
+/**
+ * Loads and applies a theme.
+ * This function:
+ * 1. Validates the theme
+ * 2. Resolves "system" to actual theme
+ * 3. Injects theme CSS
+ * 4. Sets data-theme attribute
+ * 5. Persists to localStorage
+ */
+export const loadTheme = (themeName: string): void => {
+  const validTheme = validateTheme(themeName);
+  const resolvedTheme = resolveTheme(validTheme);
+
+  injectThemeStyle(resolvedTheme);
+  setThemeAttribute(resolvedTheme);
+  setStoredTheme(validTheme); // Store original theme preference (not resolved)
+};
+
+/**
+ * Applies theme early during initial page load to prevent FOUC.
+ * Uses only localStorage and system preference (no user settings yet).
+ */
 export const applyThemeEarly = (): void => {
   const theme = getInitialTheme();
   loadTheme(theme);
 };
 
-export const loadTheme = (themeName: string): void => {
-  const validTheme = validateTheme(themeName);
+// ============================================================================
+// System Theme Listener
+// ============================================================================
 
-  // Resolve "system" to actual theme based on OS preference
-  const resolvedTheme = resolveTheme(validTheme);
-
-  // Remove existing theme
-  document.getElementById("instance-theme")?.remove();
-
-  // Apply theme (skip for default)
-  if (resolvedTheme !== "default") {
-    const css = THEME_CONTENT[resolvedTheme];
-    if (css) {
-      const style = document.createElement("style");
-      style.id = "instance-theme";
-      style.textContent = css;
-      document.head.appendChild(style);
-    }
-  }
-
-  // Set data attribute with resolved theme
-  document.documentElement.setAttribute("data-theme", resolvedTheme);
-
-  // Store theme preference (original, not resolved) for future loads
-  try {
-    localStorage.setItem("memos-theme", validTheme);
-  } catch {
-    // localStorage might not be available
-  }
-};
-
-// Sets up a listener for system theme preference changes
+/**
+ * Sets up a listener for OS-level theme preference changes.
+ * Supports both modern (addEventListener) and legacy (addListener) APIs.
+ *
+ * @param onThemeChange - Callback invoked when system theme changes
+ * @returns Cleanup function to remove the listener
+ */
 export const setupSystemThemeListener = (onThemeChange: () => void): (() => void) => {
+  // Guard against SSR
   if (typeof window === "undefined" || !window.matchMedia) {
-    return () => {}; // No-op cleanup
+    return () => {};
   }
 
   const mediaQuery = window.matchMedia("(prefers-color-scheme: dark)");
 
-  // Handle theme change
-  const handleChange = () => {
-    onThemeChange();
-  };
-
-  // Modern API (addEventListener)
+  // Modern API (preferred)
   if (mediaQuery.addEventListener) {
-    mediaQuery.addEventListener("change", handleChange);
-    return () => mediaQuery.removeEventListener("change", handleChange);
+    mediaQuery.addEventListener("change", onThemeChange);
+    return () => mediaQuery.removeEventListener("change", onThemeChange);
   }
 
-  // Legacy API (addListener) - for older browsers
+  // Legacy API (Safari < 14)
   if (mediaQuery.addListener) {
-    mediaQuery.addListener(handleChange);
-    return () => mediaQuery.removeListener(handleChange);
+    mediaQuery.addListener(onThemeChange);
+    return () => mediaQuery.removeListener(onThemeChange);
   }
 
-  return () => {}; // No-op cleanup
+  return () => {};
 };