Fix default preferred language should be an admin permitted language

CHANGELOG.txt

@@ -40,6 +40,7 @@ Changelog
  * Fix: Show the correct privacy status for child collections of private collections (Shlomo Markowitz)
  * Fix: Ensure reference index correctly handles models with primary keys not named `id` (Sage Abdullah)
  * Fix: On "move page" bulk action, do not prefill the destination with the root page (Stefan Hammer)
+ * Fix: Ensure the default preferred language respects the `WAGTAILADMIN_PERMITTED_LANGUAGES` setting (Sébastien Corbin)
  * Docs: Add missing `django.contrib.admin` to list of apps in "add to Django project" guide (Mohamed Rabiaa)
  * Docs: Add tutorial on deploying on Ubuntu to third-party tutorials (Mohammad Fathi Rahman)
  * Docs: Document that request_or_site is optional on BaseGenericSetting.load (Matt Westcott)

docs/releases/7.0.md

@@ -64,6 +64,7 @@ We have a new pagination interface for all listing views and most choosers, incl
  * Show the correct privacy status for child collections of private collections (Shlomo Markowitz)
  * Ensure reference index correctly handles models with primary keys not named `id` (Sage Abdullah)
  * On "move page" bulk action, do not prefill the destination with the root page (Stefan Hammer)
+ * Ensure the default preferred language respects the `WAGTAILADMIN_PERMITTED_LANGUAGES` setting (Sébastien Corbin)
 
 ### Documentation
 

wagtail/admin/tests/test_userbar.py

@@ -2,15 +2,18 @@ import json
 
 from django.contrib.auth.models import AnonymousUser, Permission
 from django.template import Context, Template
-from django.test import TestCase
+from django.test import TestCase, override_settings
 from django.urls import reverse
+from django.utils import translation
+from django.utils.translation import gettext
 
 from wagtail import hooks
 from wagtail.admin.userbar import AccessibilityItem
 from wagtail.coreutils import get_dummy_request
-from wagtail.models import PAGE_TEMPLATE_VAR, Page, Site
+from wagtail.models import PAGE_TEMPLATE_VAR, Locale, Page, Site
 from wagtail.test.testapp.models import BusinessChild, BusinessIndex, SimplePage
 from wagtail.test.utils import WagtailTestUtils
+from wagtail.users.models import UserProfile
 from wagtail.utils.deprecation import RemovedInWagtail80Warning
 
 
@@ -495,6 +498,56 @@ class TestUserbarInPageServe(WagtailTestUtils, TestCase):
 
             self.assertTrue(kwargs.get("called"))
 
+    @override_settings(
+        WAGTAIL_I18N_ENABLED=True,
+        WAGTAIL_CONTENT_LANGUAGES=[("en", "English"), ("fr", "French")],
+        WAGTAILADMIN_PERMITTED_LANGUAGES=[("en", "English")],
+        LANGUAGE_CODE="en",
+    )
+    def test_userbar_rendered_in_admin_permitted_language_if_user_has_no_language(self):
+        french = Locale.objects.create(language_code="fr")
+        self.homepage.copy_for_translation(french)
+        french_page = self.page.copy_for_translation(french)
+
+        with translation.override("fr"):
+            response = french_page.serve(self.request)
+            response.render()
+
+        self.assertContains(response, "Go to Wagtail admin")
+
+    @override_settings(
+        WAGTAIL_I18N_ENABLED=True,
+        WAGTAIL_CONTENT_LANGUAGES=[("en", "English"), ("fr", "French")],
+        LANGUAGE_CODE="en",
+    )
+    def test_userbar_rendered_in_active_language_if_admin_permitted(self):
+        french = Locale.objects.create(language_code="fr")
+        self.homepage.copy_for_translation(french)
+        french_page = self.page.copy_for_translation(french)
+
+        with translation.override("fr"):
+            response = french_page.serve(self.request)
+            response.render()
+
+        with translation.override("fr"):
+            expected_text = gettext("Go to Wagtail admin")
+        self.assertContains(response, expected_text)
+
+    @override_settings(LANGUAGE_CODE="en")
+    def test_userbar_rendered_in_user_preferred_language(self):
+        profile = UserProfile.get_for_user(self.user)
+        profile.preferred_language = "fr"
+        profile.save()
+
+        response = self.page.serve(self.request)
+        response.render()
+
+        # Ensure we have a French string without tests failing if translation changes
+        with translation.override("fr"):
+            expected_text = gettext("Go to Wagtail admin")
+        self.assertNotEqual(expected_text, "Go to Wagtail admin")
+        self.assertContains(response, expected_text)
+
 
 class TestUserbarHooksForChecksPanel(WagtailTestUtils, TestCase):
     def setUp(self):

wagtail/users/models.py

@@ -6,6 +6,8 @@ from django.db import models
 from django.utils.translation import get_language
 from django.utils.translation import gettext_lazy as _
 
+from wagtail.admin.localization import get_available_admin_languages
+
 
 def upload_avatar_to(instance, filename):
     filename, ext = os.path.splitext(filename)
@@ -112,7 +114,11 @@ class UserProfile(models.Model):
         return cls.objects.get_or_create(user=user)[0]
 
     def get_preferred_language(self):
-        return self.preferred_language or get_language()
+        if self.preferred_language:
+            return self.preferred_language
+        if (language := get_language()) in dict(get_available_admin_languages()):
+            return language
+        return settings.LANGUAGE_CODE
 
     def get_current_time_zone(self):
         return self.current_time_zone or settings.TIME_ZONE