topics: Fix translation issue with moved topic notifications.

Since the calls to the translation function `_()` are made outside
of the `send_message_moved_breadcrumbs` function, these strings are
translated outside of the `with override_language` block, leading to
translated strings even when we don't intend them to be translated.

We now use gettext_lazy with appropriate testing to avoid this.

zerver/lib/actions.py

@@ -35,6 +35,7 @@ from django.db.models.query import QuerySet
 from django.utils.html import escape
 from django.utils.timezone import now as timezone_now
 from django.utils.translation import gettext as _
+from django.utils.translation import gettext_lazy
 from django.utils.translation import override as override_language
 from psycopg2.extras import execute_values
 from psycopg2.sql import SQL
@@ -6489,11 +6490,13 @@ def do_update_message(
         # Notify users that the topic was moved.
         old_thread_notification_string = None
         if send_notification_to_old_thread:
-            old_thread_notification_string = _("This topic was moved by {user} to {new_location}")
+            old_thread_notification_string = gettext_lazy(
+                "This topic was moved by {user} to {new_location}"
+            )
 
         new_thread_notification_string = None
         if send_notification_to_new_thread:
-            new_thread_notification_string = _(
+            new_thread_notification_string = gettext_lazy(
                 "This topic was moved here from {old_location} by {user}"
             )
 

zerver/tests/test_message_edit.py

@@ -79,9 +79,18 @@ class EditMessageTestCase(ZulipTestCase):
             )
 
     def prepare_move_topics(
-        self, user_email: str, old_stream: str, new_stream: str, topic: str
+        self,
+        user_email: str,
+        old_stream: str,
+        new_stream: str,
+        topic: str,
+        language: Optional[str] = None,
     ) -> Tuple[UserProfile, Stream, Stream, int, int]:
         user_profile = self.example_user(user_email)
+        if language is not None:
+            user_profile.default_language = language
+            user_profile.save(update_fields=["default_language"])
+
         self.login(user_email)
         stream = self.make_stream(old_stream)
         new_stream = self.make_stream(new_stream)
@@ -1286,7 +1295,13 @@ class EditMessageTest(EditMessageTestCase):
 
     def test_move_message_to_stream(self) -> None:
         (user_profile, old_stream, new_stream, msg_id, msg_id_lt) = self.prepare_move_topics(
-            "iago", "test move stream", "new stream", "test"
+            "iago",
+            "test move stream",
+            "new stream",
+            "test",
+            # Set the user's translation language to German to test that
+            # it is overridden by the realm's default language.
+            "de",
         )
 
         result = self.client_patch(
@@ -1296,6 +1311,7 @@ class EditMessageTest(EditMessageTestCase):
                 "stream_id": new_stream.id,
                 "propagate_mode": "change_all",
             },
+            HTTP_ACCEPT_LANGUAGE="de",
         )
 
         self.assert_json_success(result)