- Integrate Flask-Babel and i18n utilities; initialize in app factory
- Add `preferred_language` to `User` with Alembic migration (011_add_user_preferred_language)
- Add `babel.cfg` and `scripts/extract_translations.py`
- Add `translations/` for en, de, fr, it, nl, fi
- Update templates to use `_()` and add language picker in navbar/profile
- Respect locale in routes and context processors; persist user preference
- Update requirements and Docker/Docker entrypoint for Babel/gettext support
- Minor copy and style adjustments across pages
Migration: run `alembic upgrade head`
