Template tag `unlocalize` does not work with `date` and `time` filters.

[Natalia Bidart]

Following #35306, it was noticed that using the date or time template filters would not honor the unlocalize template tag. See regression tests:

tests/i18n/tests.py

@@ -1351 +1351 @@
                 self.assertEqual(template2.render(context), output2)
                 self.assertEqual(template3.render(context), output3)
 
+    def test_unlocalize_honor_date_settings(self):
+        filter_template = Template(
+            "{% load l10n %}Localized: {{ my_value }}. "
+            "Unlocalized: {{ my_value|unlocalize }}."
+        )
+        tag_template = Template(
+            "{% load l10n %}Localized: {{ my_value }}. {% localize off %}"
+            "Unlocalized: {{ my_value }}{% endlocalize %}."
+        )
+        filter_inside_unlocalize = Template(
+            "{% load l10n %}Localized: {{ my_value|date }}. {% localize off %}"
+            "Unlocalized: {{ my_value|date:'DATE_FORMAT' }}{% endlocalize %}."
+        )
+        context = Context({"my_value": datetime.date(2024, 12, 15)})
+        expected_result = "Localized: 15. Dezember 2024. Unlocalized: 15-12-2024."
+        for case in (filter_template, tag_template, filter_inside_unlocalize):
+            with (
+                self.subTest(case=str(case)),
+                translation.override("de", deactivate=True),
+                self.settings(DATE_FORMAT="j-m-Y"),
+            ):
+                self.assertEqual(case.render(context), expected_result)
+
+    def test_unlocalize_honor_time_settings(self):
+        filter_template = Template(
+            "{% load l10n %}Localized: {{ my_value }}. "
+            "Unlocalized: {{ my_value|unlocalize }}."
+        )
+        tag_template = Template(
+            "{% load l10n %}Localized: {{ my_value }}. {% localize off %}"
+            "Unlocalized: {{ my_value }}{% endlocalize %}."
+        )
+        filter_inside_unlocalize = Template(
+            "{% load l10n %}Localized: {{ my_value|time }}. {% localize off %}"
+            "Unlocalized: {{ my_value|time }}{% endlocalize %}."
+        )
+        context = Context({"my_value": datetime.time(1, 2, 3)})
+        expected_result = "Localized: 01:02. Unlocalized: 01h 02m."
+        for case in (filter_template, tag_template, filter_inside_unlocalize):
+            with (
+                self.subTest(case=str(case)),
+                translation.override("de", deactivate=True),
+                self.settings(TIME_FORMAT="H\\h i\\m"),
+            ):
+                self.assertEqual(case.render(context), expected_result)
+
     def test_localized_off_numbers(self):
         """A string representation is returned for unlocalized numbers."""
         template = Template(

[Claude Paroz]

I'm not yet sure if this can be resolved in the code, or if we should rather complement the template filter docs, telling that if you apply an l10n-sensible filter inside an unlocalized section, you should specify an explicit format argument. The problem being that the way filters are currently implemented, it's not possible to transmit any context. That explains for example that floatformat gained an u parameter to force unlocalization (see #30086).

So in your example in the tests above, you should use |date:settings.DATE_FORMAT and not just DATE_FORMAT. Thoughts?