Fixed #29713 -- Added check that LANGUAGE_CODE uses standard language id format.

django/core/checks/__init__.py

@@ -12,6 +12,7 @@ import django.core.checks.security.base  # NOQA isort:skip
 import django.core.checks.security.csrf  # NOQA isort:skip
 import django.core.checks.security.sessions  # NOQA isort:skip
 import django.core.checks.templates  # NOQA isort:skip
+import django.core.checks.translation  # NOQA isort:skip
 import django.core.checks.urls  # NOQA isort:skip
 
 

django/core/checks/registry.py

@@ -15,6 +15,7 @@ class Tags:
     security = 'security'
     signals = 'signals'
     templates = 'templates'
+    translation = 'translation'
     urls = 'urls'
 
 

django/core/checks/translation.py

+import re
+
+from django.conf import settings
+from django.utils.translation.trans_real import language_code_re
+
+from . import Error, Tags, register
+
+
+@register(Tags.translation)
+def check_setting_language_code(app_configs, **kwargs):
+    """
+    Errors if language code is in the wrong format. Language codes specification outlined by
+    https://en.wikipedia.org/wiki/IETF_language_tag#Syntax_of_language_tags
+    """
+    match_result = re.match(language_code_re, settings.LANGUAGE_CODE)
+    errors = []
+    if not match_result:
+        errors.append(Error(
+            "LANGUAGE_CODE in settings.py is {}. It should be in the form ll or ll-cc where ll is the language and cc "
+            "is the country. Examples include: it, de-at, es, pt-br. The full set of language codes specifications is "
+            "outlined by https://en.wikipedia.org/wiki/IETF_language_tag#Syntax_of_language_tags".format(
+                settings.LANGUAGE_CODE),
+            id="translation.E001",
+        ))
+    return errors

docs/ref/checks.txt

@@ -86,6 +86,7 @@ Django's system checks are organized using the following tags:
 * ``staticfiles``: Checks :mod:`django.contrib.staticfiles` configuration.
 * ``templates``: Checks template related configuration.
 * ``urls``: Checks URL configuration.
+* ``translation``: Checks language formats used for translation.
 
 Some checks may be registered with multiple tags.
 
@@ -449,6 +450,18 @@ The following checks are performed on your URL configuration:
 * **urls.E006**: The :setting:`MEDIA_URL`/ :setting:`STATIC_URL` setting must
   end with a slash.
 
+Translation
+-----------
+
+The following checks are performed on your translation configuration:
+
+* **translation.E001**: LANGUAGE_CODE in settings.py is ``<language_code>``.
+   It should be in the form ll or ll-cc where ll is the language and cc is the
+   country. Examples include: ``it``, ``de-at``, ``es``, ``pt-br``. The full
+   set of language codes specifications is outlined by
+   https://en.wikipedia.org/wiki/IETF_language_tag#Syntax_of_language_tags
+
+
 ``contrib`` app checks
 ======================
 

tests/check_framework/test_translation.py

+from django.core.checks.translation import check_setting_language_code
+from django.test import SimpleTestCase, override_settings
+
+
+class TranslationCheckTests(SimpleTestCase):
+
+    @override_settings(LANGUAGE_CODE="eu")
+    def test_valid_language_code_format_ll_only(self):
+        result = check_setting_language_code(None)
+        self.assertEqual(len(result), 0)
+
+    @override_settings(LANGUAGE_CODE="eü")
+    def test_invalid_language_code_format_ll_only(self):
+        result = check_setting_language_code(None)
+        self.assertEqual(len(result), 1)
+        error = result[0]
+        self.assertEqual(error.id, 'translation.E001')
+        self.assertEqual(error.msg, (
+            "LANGUAGE_CODE in settings.py is eü. It should be in the form ll or ll-cc where ll is the language and cc "
+            "is the country. Examples include: it, de-at, es, pt-br. The full set of language codes specifications is "
+            "outlined by https://en.wikipedia.org/wiki/IETF_language_tag#Syntax_of_language_tags"
+        ))
+
+    @override_settings(LANGUAGE_CODE="en-US")
+    def test_valid_language_code_format_ll_cc(self):
+        result = check_setting_language_code(None)
+        self.assertEqual(len(result), 0)
+
+    @override_settings(LANGUAGE_CODE="en_US")
+    def test_invalid_language_code_format_ll_cc(self):
+        result = check_setting_language_code(None)
+        self.assertEqual(len(result), 1)
+        error = result[0]
+        self.assertEqual(error.id, 'translation.E001')
+        self.assertEqual(error.msg, (
+            "LANGUAGE_CODE in settings.py is en_US. It should be in the form ll or ll-cc where ll is the language and "
+            "cc is the country. Examples include: it, de-at, es, pt-br. The full set of language codes specifications "
+            "is outlined by https://en.wikipedia.org/wiki/IETF_language_tag#Syntax_of_language_tags"
+        ))

tests/i18n/tests.py

@@ -1649,6 +1649,7 @@ class CountrySpecificLanguageTests(SimpleTestCase):
         self.assertTrue(check_for_language('en'))
         self.assertTrue(check_for_language('en-us'))
         self.assertTrue(check_for_language('en-US'))
+        self.assertFalse(check_for_language('en_US'))
         self.assertTrue(check_for_language('be'))
         self.assertTrue(check_for_language('be@latin'))
         self.assertTrue(check_for_language('sr-RS@latin'))