Replaces the Store-only DE/EN toggle with an app-wide one
parked in the sidebar footer next to the theme button.
Pressing it flips every translated string at once: nav
labels, page titles, common buttons, the bilingual
store-index content.
Implementation:
- Adds `flutter_localizations` + `intl` to pubspec, plus
`flutter.generate: true` so `flutter gen-l10n` runs in the
build pipeline.
- ARB sources at `lib/l10n/app_en.arb` and `app_de.arb`. The
EN file is the template; DE carries the German strings.
Initial coverage: navigation, common buttons, page titles,
channels / store / audit / modules / approvals headers,
hub-unreachable copy, MCP + n8n panel headers + hints.
Rest of the UI strings are still English-literal — those
fall in incrementally as we touch each surface.
- Generated `AppLocalizations` lives at
`lib/l10n/app_localizations*.dart` (regenerated via
`flutter gen-l10n` on every ARB edit).
- `StudioAppState` gains `localeNotifier` alongside
`modeNotifier`; persisted via SharedPreferences key
`locale.code`.
- Sidebar `_LanguageToggle` reads/writes through the
notifier. The Store's per-page locale state is gone:
`_locale` now reads `Localizations.localeOf(context)
.languageCode`, so the bilingual store-index content
follows the global setting without a second toggle.
- `_NavPage.label` becomes `_NavPage.id` + `labelOf(context)`;
Cmd+K palette and Sidebar both read the localized label.
Out of scope this iteration: localizing the remaining
~80% of UI strings (Settings dialog labels, Store search
hint, error messages). Those land incrementally — the i18n
infrastructure now means each is a one-line ARB edit + one
call-site swap.
Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>
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