feat(i18n): add da/en locale pipeline and shared backend key resolver

lobby/i18n.py

@@ -1,8 +1,12 @@
 import json
+import logging
 from functools import lru_cache
 from pathlib import Path
 
-from django.http import JsonResponse
+from django.http import HttpRequest, JsonResponse
+from django.utils.translation import get_language_from_request
+
+LOGGER = logging.getLogger(__name__)
 
 
 @lru_cache(maxsize=1)
@@ -12,9 +16,55 @@ def lobby_i18n_catalog() -> dict:
         return json.load(handle)
 
 
+@lru_cache(maxsize=1)
+def i18n_locale_config() -> tuple[str, tuple[str, ...]]:
+    locales = lobby_i18n_catalog().get("locales", {})
+    default_locale = str(locales.get("default", "en")).strip().lower() or "en"
+    supported_locales = tuple(
+        locale.strip().lower() for locale in locales.get("supported", ["en", "da"]) if str(locale).strip()
+    ) or ("en", "da")
+    return default_locale, supported_locales
+
+
 def lobby_i18n_errors() -> dict:
     return lobby_i18n_catalog().get("backend", {}).get("error_codes", {})
 
 
-def api_error(*, code: str, message: str, status: int) -> JsonResponse:
-    return JsonResponse({"error": message, "error_code": code}, status=status)
+def lobby_i18n_error_messages() -> dict:
+    return lobby_i18n_catalog().get("backend", {}).get("errors", {})
+
+
+def resolve_locale(request: HttpRequest) -> str:
+    default_locale, supported_locales = i18n_locale_config()
+    requested = (get_language_from_request(request) or "").split("-", 1)[0].lower()
+    if requested in supported_locales:
+        return requested
+    return default_locale
+
+
+def resolve_error_message(*, key: str, locale: str) -> str:
+    default_locale, _supported_locales = i18n_locale_config()
+    translations = lobby_i18n_error_messages().get(key)
+    if not isinstance(translations, dict):
+        LOGGER.warning("i18n key missing in shared catalog", extra={"key": key, "locale": locale})
+        return key
+
+    if locale in translations and translations[locale]:
+        return translations[locale]
+    if default_locale in translations and translations[default_locale]:
+        return translations[default_locale]
+
+    LOGGER.warning("i18n translation missing for key", extra={"key": key, "locale": locale})
+    return key
+
+
+def api_error(request: HttpRequest, *, key: str, status: int) -> JsonResponse:
+    locale = resolve_locale(request)
+    return JsonResponse(
+        {
+            "error": resolve_error_message(key=key, locale=locale),
+            "error_code": key,
+            "locale": locale,
+        },
+        status=status,
+    )