- Add frontend/src/lang/translations/ja.json (full translation of all 422 entries from en.json)
- Register ja in frontend/src/lang/index.js so it appears in the language selector
Tested locally with v2.2.3 build. UI strings render correctly in Japanese.
Closes: language support request
Co-authored-by: Taro Kawakami <tarokun@tunagufactory.jp>