API: Fix locale accidentally being a required field

src/pretix/api/serializers/order.py

@@ -1102,7 +1102,7 @@ class OrderCreateSerializer(I18nAwareModelSerializer):
         queryset=SalesChannel.objects.none(),
         required=False,
     )
-    locale = serializers.ChoiceField(choices=[])
+    locale = serializers.ChoiceField(choices=[], required=False, allow_null=True)
 
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)

src/pretix/api/serializers/waitinglist.py

@@ -27,7 +27,7 @@ from pretix.base.models import WaitingListEntry
 
 
 class WaitingListSerializer(I18nAwareModelSerializer):
-    locale = serializers.ChoiceField(choices=[])
+    locale = serializers.ChoiceField(choices=[], required=False, allow_null=True)
 
     class Meta:
         model = WaitingListEntry
@@ -66,4 +66,7 @@ class WaitingListSerializer(I18nAwareModelSerializer):
         if data.get('name_parts') and '_scheme' not in data.get('name_parts'):
             data['name_parts']['_scheme'] = event.settings.name_scheme
 
+        if data.get('locale', None) is None:
+            data['locale'] = event.settings.locale
+
         return data

src/tests/api/test_order_create.py

@@ -622,6 +622,23 @@ def test_order_create_sales_channel_invalid(token_client, organizer, event, item
     assert resp.data == {'sales_channel': ['Object with identifier=foo does not exist.']}
 
 
+@pytest.mark.django_db
+def test_order_create_locale_optional(token_client, organizer, event, item, quota, question):
+    event.settings.locale = "de"
+    event.settings.locales = ["en", "de"]
+    res = copy.deepcopy(ORDER_CREATE_PAYLOAD)
+    del res['locale']
+    res['positions'][0]['item'] = item.pk
+    res['positions'][0]['answers'][0]['question'] = question.pk
+    resp = token_client.post(
+        '/api/v1/organizers/{}/events/{}/orders/'.format(
+            organizer.slug, event.slug
+        ), format='json', data=res
+    )
+    assert resp.status_code == 201
+    assert resp.data["locale"] == event.settings.locale
+
+
 @pytest.mark.django_db
 def test_order_create_locale_invalid(token_client, organizer, event, item, quota, question):
     res = copy.deepcopy(ORDER_CREATE_PAYLOAD)

src/tests/api/test_waitinglist.py

@@ -469,3 +469,21 @@ def test_wle_send_voucher_unavailable(token_client, organizer, event, item, wle,
     assert resp.status_code == 400
     wle.refresh_from_db()
     assert not wle.voucher
+
+
+@pytest.mark.django_db
+def test_wle_locale_optional(token_client, organizer, event, item, quota):
+    event.settings.locale = "de"
+    event.settings.locales = ["en", "de"]
+    quota.size = 0
+    quota.save()
+    wle = create_wle(
+        token_client, organizer, event,
+        data={
+            'email': 'testdummy@pretix.eu',
+            'item': item.pk,
+            'variation': None,
+            'subevent': None
+        },
+    )
+    assert wle.locale == "de"