- STRINGS object in app.js with all UI strings in de/en/pl
- tr() function, ldoc() locale-aware date formatting
- tpl() auto-translates data-t/data-ph/data-val attributes on clone
- app.html.twig: data-t attributes on all template static text, language picker in data menu
- locale CHAR(2) column on users table; GET /api/me returns locale; PATCH /api/me accepts locale
- setLocale() persists to API + localStorage; applyLocale() reads user.locale → localStorage → navigator.language
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
