Add an empty choice for the Locale filter for choosers

it is optional after all

wagtail/admin/forms/choosers.py

@@ -133,13 +133,13 @@ class LocaleFilterMixin(forms.Form):
 
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
-        locales = Locale.objects.all()
-        if locales:
-            self.fields["locale"] = forms.ChoiceField(
-                choices=[
+        choices = [
             (locale.language_code, locale.get_display_name())
-                    for locale in locales
-                ],
+            for locale in Locale.objects.all()
+        ]
+        if choices:
+            self.fields["locale"] = forms.ChoiceField(
+                choices=[("", _("All")), *choices],
                 required=False,
                 widget=forms.Select(attrs={"data-chooser-modal-search-filter": True}),
             )

wagtail/admin/tests/viewsets/test_chooser_viewset.py

@@ -1,17 +1,19 @@
 import json
 
-from django.test import TestCase
+from django.test import TestCase, override_settings
+from django.urls import reverse
 
 from wagtail.admin import widgets
+from wagtail.models import Locale
+from wagtail.test.snippets.models import TranslatableSnippet
 from wagtail.test.testapp.models import Advert
 from wagtail.test.testapp.views import AdvertChooserWidget
 from wagtail.test.utils.wagtail_tests import WagtailTestUtils
 
 
 class TestChooserViewSetWithFilteredObjects(WagtailTestUtils, TestCase):
-    def setUp(self):
-        self.user = self.login()
-
+    @classmethod
+    def setUpTestData(cls):
         Advert.objects.create(text="Head On, apply directly to the forehead")
 
         advert2 = Advert.objects.create(
@@ -19,6 +21,9 @@ class TestChooserViewSetWithFilteredObjects(WagtailTestUtils, TestCase):
         )
         advert2.tags.add("animated")
 
+    def setUp(self):
+        self.user = self.login()
+
     def test_get(self):
         response = self.client.get("/admin/animated_advert_chooser/")
         response_html = json.loads(response.content)["html"]
@@ -54,3 +59,32 @@ class TestChooserViewSetWithFilteredObjects(WagtailTestUtils, TestCase):
                 "linkedFields": {"url": "#id_cool_url"},
             },
         )
+
+    @override_settings(WAGTAIL_I18N_ENABLED=True)
+    def test_filter_by_locale(self):
+        fr_locale = Locale.objects.create(language_code="fr")
+
+        TranslatableSnippet.objects.create(text="English snippet")
+        TranslatableSnippet.objects.create(text="French snippet", locale=fr_locale)
+
+        chooser_url = reverse(
+            "wagtailsnippetchoosers_snippetstests_translatablesnippet:choose"
+        )
+        response = self.client.get(chooser_url)
+        self.assertEqual(response.status_code, 200)
+        soup = self.get_soup(json.loads(response.content)["html"])
+
+        options = soup.select("select[name=locale] option")
+        self.assertEqual(len(options), 3)
+        self.assertListEqual(
+            [(option["value"], option.text) for option in options],
+            [("", "All"), ("en", "English"), ("fr", "French")],
+        )
+
+        self.assertEqual(len(response.context["results"]), 2)
+        self.assertEqual(response.context["results"][0].text, "English snippet")
+        self.assertEqual(response.context["results"][1].text, "French snippet")
+
+        response = self.client.get(f"{chooser_url}?locale=en")
+        self.assertEqual(len(response.context["results"]), 1)
+        self.assertEqual(response.context["results"][0].text, "English snippet")