weirsoe-party-protocol/docs/I18N_ARCHITECTURE.md

Shared i18n architecture (frontend + backend)

Scope

Issue #175 requires one shared i18n contract for MVP host/player flows across frontend and backend.

Source of truth

• Catalog: shared/i18n/lobby.json
• Locales:
  • supported: en, da
  • default/fallback: en

Django (lobby/i18n.py) reads directly from the catalog. Frontend runtimes are Angular-first and use a shared loader (frontend/shared/i18n/lobby-loader.ts) so Angular shell and SPA fallback consume the same keyspace + locale normalization.

Key naming convention

• Domain-first namespaces:
  • frontend.ui.common.*
  • frontend.ui.host.*
  • frontend.ui.player.*
  • frontend.errors.*
  • backend.errors.*
  • backend.error_codes.*
• UI lookup keys in Angular are shortened aliases mapped under frontend.ui, e.g.:
  • host.start_round
  • player.submit_guess
  • common.session_code
• Backend API errors return stable code + localized message:
  • error_code = machine-stable key from backend.error_codes
  • error = localized message from backend.errors
  • locale = resolved request locale

Fallback model (robust)

1. Resolve requested locale (Accept-Language on backend, user/browser preference on frontend).
2. If locale unsupported -> use default en.
3. If key missing -> return key and log warning.
4. If locale translation missing for key -> fallback to en translation.

Audio-routing policy

• Catalog capability: frontend.capabilities.client_has_no_audio_output = true
• Host/player clients expose this as a read-only capability flag.
• Policy: phone clients must not play audio directly; only primary/host output is allowed.

Verification

• Backend tests: lobby/tests.py i18n coverage for locale selection + fallback + error-code/message matrix.
• Frontend smoke/e2e-level unit coverage:
  • frontend/angular/src/app/lobby-i18n.spec.ts
  • frontend/angular/src/app/i18n-mvp-flow-smoke.spec.ts
  • frontend/angular/src/app/features/host/host-shell.component.spec.ts
  • frontend/angular/src/app/features/player/player-shell.component.spec.ts
  • frontend/tests/lobby-loader.parity.test.ts (minimal da/en key parity guard for shared keyspace)