Fixed #22120 -- Documented persistent activation of languages and cleaned up language session key use

django/contrib/auth/__init__.py

@@ -5,6 +5,7 @@ from django.apps import apps as django_apps
 from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured, PermissionDenied
 from django.utils.module_loading import import_string
+from django.utils.translation import LANGUAGE_SESSION_KEY
 from django.middleware.csrf import rotate_token
 
 from .signals import user_logged_in, user_logged_out, user_login_failed
@@ -108,12 +109,12 @@ def logout(request):
 
     # remember language choice saved to session
     # for backwards compatibility django_language is also checked (remove in 1.8)
-    language = request.session.get('_language', request.session.get('django_language'))
+    language = request.session.get(LANGUAGE_SESSION_KEY, request.session.get('django_language'))
 
     request.session.flush()
 
     if language is not None:
-        request.session['_language'] = language
+        request.session[LANGUAGE_SESSION_KEY] = language
 
     if hasattr(request, 'user'):
         from django.contrib.auth.models import AnonymousUser

django/contrib/auth/tests/test_views.py

@@ -14,6 +14,7 @@ from django.http import QueryDict, HttpRequest
 from django.utils.encoding import force_text
 from django.utils.http import urlquote
 from django.utils.six.moves.urllib.parse import urlparse, ParseResult
+from django.utils.translation import LANGUAGE_SESSION_KEY
 from django.utils._os import upath
 from django.test import TestCase, override_settings
 from django.test.utils import patch_logger
@@ -718,12 +719,12 @@ class LogoutTest(AuthViewsTestCase):
         # Create a new session with language
         engine = import_module(settings.SESSION_ENGINE)
         session = engine.SessionStore()
-        session['_language'] = 'pl'
+        session[LANGUAGE_SESSION_KEY] = 'pl'
         session.save()
         self.client.cookies[settings.SESSION_COOKIE_NAME] = session.session_key
 
         self.client.get('/logout/')
-        self.assertEqual(self.client.session['_language'], 'pl')
+        self.assertEqual(self.client.session[LANGUAGE_SESSION_KEY], 'pl')
 
 
 @skipIfCustomUser

django/utils/translation/__init__.py

@@ -21,6 +21,7 @@ __all__ = [
     'npgettext', 'npgettext_lazy',
 ]
 
+LANGUAGE_SESSION_KEY = '_language'
 
 class TranslatorCommentWarning(SyntaxWarning):
     pass

django/utils/translation/trans_real.py

@@ -18,7 +18,7 @@ from django.utils._os import upath
 from django.utils.safestring import mark_safe, SafeData
 from django.utils import six, lru_cache
 from django.utils.six import StringIO
-from django.utils.translation import TranslatorCommentWarning, trim_whitespace
+from django.utils.translation import TranslatorCommentWarning, trim_whitespace, LANGUAGE_SESSION_KEY
 
 
 # Translations are cached in a dictionary for every language+app tuple.
@@ -478,7 +478,7 @@ def get_language_from_request(request, check_path=False):
 
     if hasattr(request, 'session'):
         # for backwards compatibility django_language is also checked (remove in 1.8)
-        lang_code = request.session.get('_language', request.session.get('django_language'))
+        lang_code = request.session.get(LANGUAGE_SESSION_KEY, request.session.get('django_language'))
         if lang_code in supported and lang_code is not None and check_for_language(lang_code):
             return lang_code
 

django/views/i18n.py

@@ -7,7 +7,7 @@ from django import http
 from django.apps import apps
 from django.conf import settings
 from django.template import Context, Template
-from django.utils.translation import check_for_language, to_locale, get_language
+from django.utils.translation import check_for_language, to_locale, get_language, LANGUAGE_SESSION_KEY
 from django.utils.encoding import smart_text
 from django.utils.formats import get_format_modules, get_format
 from django.utils._os import upath
@@ -36,7 +36,7 @@ def set_language(request):
         lang_code = request.POST.get('language', None)
         if lang_code and check_for_language(lang_code):
             if hasattr(request, 'session'):
-                request.session['_language'] = lang_code
+                request.session[LANGUAGE_SESSION_KEY] = lang_code
             else:
                 response.set_cookie(settings.LANGUAGE_COOKIE_NAME, lang_code)
     return response