Translate errors for addon selection

src/pretix/base/services/cart.py

@@ -10,7 +10,7 @@ from django.dispatch import receiver
 from django.utils.timezone import now
 from django.utils.translation import pgettext_lazy, ugettext as _
 
-from pretix.base.i18n import LazyLocaleException, language
+from pretix.base.i18n import language
 from pretix.base.models import (
     CartPosition, Event, InvoiceAddress, Item, ItemVariation, Voucher,
 )
@@ -27,8 +27,16 @@ from pretix.presale.signals import (
 )
 
 
-class CartError(LazyLocaleException):
-    pass
+class CartError(Exception):
+    def __init__(self, *args):
+        msg = args[0]
+        msgargs = args[1] if len(args) > 1 else None
+        self.args = args
+        if msgargs:
+            msg = _(msg) % msgargs
+        else:
+            msg = _(msg)
+        super().__init__(msg)
 
 
 error_messages = {

src/pretix/presale/checkoutflow.py

@@ -6,7 +6,9 @@ from django.http import HttpResponseNotAllowed, JsonResponse
 from django.shortcuts import redirect
 from django.utils import translation
 from django.utils.functional import cached_property
-from django.utils.translation import pgettext_lazy, ugettext_lazy as _
+from django.utils.translation import (
+    get_language, pgettext_lazy, ugettext_lazy as _,
+)
 from django.views.generic.base import TemplateResponseMixin
 
 from pretix.base.models import Order
@@ -292,7 +294,7 @@ class AddOnsStep(CartMixin, AsyncAction, TemplateFlowStep):
             return self.get(request, *args, **kwargs)
 
         return self.do(self.request.event.id, data, get_or_create_cart_id(self.request),
-                       invoice_address=self.invoice_address.pk)
+                       invoice_address=self.invoice_address.pk, locale=get_language())
 
 
 class QuestionsStep(QuestionsViewMixin, CartMixin, TemplateFlowStep):