# Issue #205 — Django i18n foundation (da/en)

## Implemented acceptance checks

- **Django i18n setup for `en` + `da` with `en` fallback**
  - `LANGUAGE_CODE` set to `en`.
  - `LANGUAGES = [('en', 'English'), ('da', 'Danish')]`.
  - `LocaleMiddleware` enabled in middleware chain.
- **Shared-key resolver/adapter (no ad hoc backend mapping)**
  - Backend error responses now resolve from shared catalog keys in `shared/i18n/lobby.json`.
  - `lobby.i18n.api_error()` accepts a shared key and resolves locale-specific text.
- **Representative API flow documented with key/locale behavior**
  - `POST /lobby/join` with empty code returns:
    - `error_code: "session_code_required"`
    - localized `error`
    - resolved `locale`
- **Missing key handling deterministic and loggable**
  - `resolve_error_message()` returns key string when key/translation is missing.
  - Warning is logged (`lobby.i18n` logger) for missing key/translation.

## Example response behavior

### Request
`POST /lobby/join` with empty code and header `Accept-Language: da`

### Response (400)

```json
{
  "error": "Sessionskode er påkrævet",
  "error_code": "session_code_required",
  "locale": "da"
}
```

If locale is unsupported (e.g. `fr`), response uses `locale: "en"` and English message.