[common] Respect user language in Orga backend

src/pretalx/common/middleware.py

@@ -1,6 +1,11 @@
+import pytz
+from django.conf import settings
 from django.core.exceptions import PermissionDenied
 from django.shortcuts import redirect
 from django.urls import resolve
+from django.utils import translation, timezone
+from django.utils.translation.trans_real import parse_accept_lang_header, language_code_re, \
+    get_supported_language_variant
 
 from pretalx.event.models import Event
 from pretalx.person.models import EventPermission
@@ -47,4 +52,64 @@ def __call__(self, request):
             if hasattr(request, 'event') and not request.is_orga:
                 raise PermissionDenied()
 
+            self._select_locale(request)
+
         return self.get_response(request)
+
+    def _select_locale(self, request):
+        supported = request.event.locales if hasattr(request, 'event') else settings.LANGUAGES
+        language = (
+            self._language_from_user(request, supported)
+            or self._language_from_browser(request, supported)
+        )
+        if hasattr(request, 'event'):
+            language = language or request.event.locale
+
+        translation.activate(language)
+        request.LANGUAGE_CODE = translation.get_language()
+
+        try:
+            if request.user.is_authenticated:
+                tzname = request.user.timezone
+            elif hasattr(request, 'event'):
+                tzname = request.event.timezone
+            else:
+                tzname = settings.TIME_ZONE
+            timezone.activate(pytz.timezone(tzname))
+            request.timezone = tzname
+        except pytz.UnknownTimeZoneError:
+            pass
+
+    def _language_from_browser(self, request, supported):
+        accept_value = request.META.get('HTTP_ACCEPT_LANGUAGE', '')
+        for accept_lang, unused in parse_accept_lang_header(accept_value):
+            if accept_lang == '*':
+                break
+
+            if not language_code_re.search(accept_lang):
+                continue
+
+            try:
+                val = get_supported_language_variant(accept_lang)
+                if val and val in supported:
+                    return val
+            except LookupError:
+                continue
+
+    def _language_from_cookie(self, request, supported):
+        cookie_value = request.COOKIES.get(settings.LANGUAGE_COOKIE_NAME)
+        try:
+            cookie_value = get_supported_language_variant(cookie_value)
+            if cookie_value and cookie_value in supported:
+                return cookie_value
+        except LookupError:
+            pass
+
+    def _language_from_user(self, request, supported):
+        if request.user.is_authenticated:
+            try:
+                value = get_supported_language_variant(request.user.locale)
+                if value and value in supported:
+                    return value
+            except LookupError:
+                pass