Account.Locale gorm default was changed from 'en' to 'zh_CN' in the
locale cleanup commit (a1ae852), but the default-values test still
asserted 'en', causing TestAccountDefaultValues to fail. Align the
assertion with the new default.
- widget/i18n/index.js: only import en.json and zh_CN.json (the only
locale files present); remove 40+ imports for missing locale JSONs
that caused Vite compile failure and global white screen
- dashboard/i18n/index.js: remove unused locale imports for consistency
- Remove 62 unused locale JSON files from widget/i18n/locale/
- Minor: update index.html, test helpers, e2e test, languages spec