Widget: Fix language on first iframe request

src/pretix/api/auth/session.py

@@ -20,7 +20,9 @@
 # <https://www.gnu.org/licenses/>.
 #
 from rest_framework import exceptions
-from rest_framework.authentication import SessionAuthentication as BaseSessionAuthentication
+from rest_framework.authentication import (
+    SessionAuthentication as BaseSessionAuthentication,
+)
 
 from pretix.multidomain.middlewares import CsrfViewMiddleware
 

src/pretix/base/middleware.py

@@ -44,6 +44,25 @@ from pretix.multidomain.urlreverse import (
 _supported = None
 
 
+def get_supported_language(requested_language, allowed_languages, default_language):
+    language = requested_language
+    if language not in allowed_languages:
+        firstpart = language.split('-')[0]
+        if firstpart in allowed_languages:
+            language = firstpart
+        else:
+            language = default_language
+            for lang in allowed_languages:
+                if lang.startswith(firstpart + '-'):
+                    language = lang
+                    break
+    if language not in allowed_languages:
+        # This seems redundant, but can happen in the rare edge case that settings.locale is (wrongfully)
+        # not part of settings.locales
+        language = allowed_languages[0]
+    return language
+
+
 class LocaleMiddleware(MiddlewareMixin):
 
     """
@@ -65,20 +84,11 @@ class LocaleMiddleware(MiddlewareMixin):
                 settings_holder = None
 
             if settings_holder:
-                if language not in settings_holder.settings.locales:
-                    firstpart = language.split('-')[0]
-                    if firstpart in settings_holder.settings.locales:
-                        language = firstpart
-                    else:
-                        language = settings_holder.settings.locale
-                        for lang in settings_holder.settings.locales:
-                            if lang.startswith(firstpart + '-'):
-                                language = lang
-                                break
-                if language not in settings_holder.settings.locales:
-                    # This seems redundant, but can happen in the rare edge case that settings.locale is (wrongfully)
-                    # not part of settings.locales
-                    language = settings_holder.settings.locales[0]
+                language = get_supported_language(
+                    language,
+                    settings_holder.settings.locales,
+                    settings_holder.settings.locale,
+                )
                 if '-' not in language and settings_holder.settings.region:
                     language += '-' + settings_holder.settings.region
         else:

src/pretix/presale/views/__init__.py

@@ -41,12 +41,14 @@ from itertools import groupby
 from django.conf import settings
 from django.contrib import messages
 from django.db.models import Exists, OuterRef, Prefetch, Sum
+from django.utils import translation
 from django.utils.functional import cached_property
 from django.utils.timezone import now
 from django.utils.translation import gettext_lazy as _
 from django_scopes import scopes_disabled
 
-from pretix.base.i18n import language
+from pretix.base.i18n import get_language_without_region
+from pretix.base.middleware import get_supported_language
 from pretix.base.models import (
     CartPosition, Customer, InvoiceAddress, ItemAddOn, Question,
     QuestionAnswer, QuestionOption, TaxRule,
@@ -455,11 +457,24 @@ def iframe_entry_view_wrapper(view_func):
 
         locale = request.GET.get('locale')
         if locale and locale in [lc for lc, ll in settings.LANGUAGES]:
-            region = None
+            lng = locale
             if hasattr(request, 'event'):
+                lng = get_supported_language(
+                    lng,
+                    request.event.settings.locales,
+                    request.event.settings.locale,
+                )
+
                 region = request.event.settings.region
-            with language(locale, region):
-                resp = view_func(request, *args, **kwargs)
+                if '-' not in lng and region:
+                    lng += '-' + region.lower()
+
+            # with language() is not good enough here – we really need to take the role of LocaleMiddleware and modify
+            # global state, because template rendering might be happening lazily.
+            translation.activate(lng)
+            request.LANGUAGE_CODE = get_language_without_region()
+            resp = view_func(request, *args, **kwargs)
+
             max_age = 10 * 365 * 24 * 60 * 60
             set_cookie_without_samesite(
                 request,