Enable `ja` language in docs

docs/en/mkdocs.yml

@@ -317,6 +317,8 @@ extra:
     name: de - Deutsch
   - link: /es/
     name: es - español
+  - link: /ja/
+    name: ja - 日本語
   - link: /pt/
     name: pt - português
   - link: /ru/

scripts/docs.py

@@ -23,6 +23,7 @@ SUPPORTED_LANGS = {
     "en",
     "de",
     "es",
+    "ja",
     "pt",
     "ru",
 }