Fixed #5789 -- Changed LocaleMiddleware session variable to '_language'.

The old 'django_language' variable will still be read from in order
to migrate users. The backwards-compatability shim will be removed in
Django 1.8.

Thanks to jdunck for the report and stugots for the initial patch.

8 files changed, 58 insertions, 14 deletions

diff --git a/django/middleware/locale.py b/django/middleware/locale.py
index bcdead5897..87f904d7dd 100644
--- a/django/middleware/locale.py
+++ b/django/middleware/locale.py
@@ -56,8 +56,14 @@ class LocaleMiddleware(object):
                 return self.response_redirect_class(language_url)
 
         # Store language back into session if it is not present
-        if hasattr(request, 'session'):
-            request.session.setdefault('django_language', language)
+        if hasattr(request, 'session') and '_language' not in request.session:
+            # Backwards compatibility check on django_language (remove in 1.8);
+            # revert to: `request.session.setdefault('_language', language)`.
+            if 'django_language' in request.session:
+                request.session['_language'] = request.session['django_language']
+                del request.session['django_language']
+            else:
+                request.session['_language'] = language
 
         if not (self.is_language_prefix_patterns_used()
                 and language_from_path):
diff --git a/django/utils/translation/trans_real.py b/django/utils/translation/trans_real.py
index c7b41fa373..c8c7bddb14 100644
--- a/django/utils/translation/trans_real.py
+++ b/django/utils/translation/trans_real.py
@@ -426,7 +426,8 @@ def get_language_from_request(request, check_path=False):
             return lang_code
 
     if hasattr(request, 'session'):
-        lang_code = request.session.get('django_language', None)
+        # for backwards compatibility django_language is also checked (remove in 1.8)
+        lang_code = request.session.get('_language', 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
 
diff --git a/django/views/i18n.py b/django/views/i18n.py
index 86acb9c032..2623a00d6a 100644
--- a/django/views/i18n.py
+++ b/django/views/i18n.py
@@ -34,7 +34,7 @@ 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['django_language'] = lang_code
+                request.session['_language'] = lang_code
             else:
                 response.set_cookie(settings.LANGUAGE_COOKIE_NAME, lang_code)
     return response
diff --git a/docs/internals/deprecation.txt b/docs/internals/deprecation.txt
index bf26d8d855..42b81419ec 100644
--- a/docs/internals/deprecation.txt
+++ b/docs/internals/deprecation.txt
@@ -410,6 +410,9 @@ these changes.
 * The ``Model._meta.get_(add|change|delete)_permission`` methods will
   be removed.
 
+* The session key ``django_language`` will no longer be read for backwards
+  compatibility.
+
 1.9
 ---
 
diff --git a/docs/releases/1.7.txt b/docs/releases/1.7.txt
index d5c1f886da..699566f1d3 100644
--- a/docs/releases/1.7.txt
+++ b/docs/releases/1.7.txt
@@ -302,6 +302,13 @@ Internationalization
 * The :attr:`django.middleware.locale.LocaleMiddleware.response_redirect_class`
   attribute allows you to customize the redirects issued by the middleware.
 
+* The :class:`~django.middleware.locale.LocaleMiddleware` now stores the user's
+  selected language with the session key ``_language``. Previously it was
+  stored with the key ``django_language``, but keys reserved for Django should
+  start with an underscore. For backwards compatibility ``django_language`` is
+  still read from in 1.7. Sessions will be migrated to the new ``_language``
+  key as they are written.
+
 Management Commands
 ^^^^^^^^^^^^^^^^^^^
 
diff --git a/docs/topics/i18n/translation.txt b/docs/topics/i18n/translation.txt
index d8c2b49724..08e87b1425 100644
--- a/docs/topics/i18n/translation.txt
+++ b/docs/topics/i18n/translation.txt
@@ -1594,8 +1594,13 @@ following this algorithm:
   root URLconf. See :ref:`url-internationalization` for more information
   about the language prefix and how to internationalize URL patterns.
 
-* Failing that, it looks for a ``django_language`` key in the current
-  user's session.
+* Failing that, it looks for a ``_language`` key in the current user's session.
+
+  .. versionchanged:: 1.7
+
+      In previous versions, the key was named ``django_language`` but it was
+      renamed to start with an underscore to denote a Django reserved session
+      key.
 
 * Failing that, it looks for a cookie.
 
diff --git a/tests/i18n/tests.py b/tests/i18n/tests.py
index 7cef9e1716..fbb3476f91 100644
--- a/tests/i18n/tests.py
+++ b/tests/i18n/tests.py
@@ -1190,17 +1190,39 @@ class LocaleMiddlewareTests(TransRealMixin, TestCase):
 
         # Clear the session data before request
         session.save()
-        self.client.get('/en/simple/')
-        self.assertEqual(self.client.session['django_language'], 'en')
+        response = self.client.get('/en/simple/')
+        self.assertEqual(self.client.session['_language'], 'en')
 
         # Clear the session data before request
         session.save()
-        self.client.get('/fr/simple/')
-        self.assertEqual(self.client.session['django_language'], 'fr')
+        response = self.client.get('/fr/simple/')
+        self.assertEqual(self.client.session['_language'], 'fr')
 
         # Check that language is not changed in session
-        self.client.get('/en/simple/')
-        self.assertEqual(self.client.session['django_language'], 'fr')
+        response = self.client.get('/en/simple/')
+        self.assertEqual(self.client.session['_language'], 'fr')
+
+    @override_settings(
+        MIDDLEWARE_CLASSES=(
+            'django.contrib.sessions.middleware.SessionMiddleware',
+            'django.middleware.locale.LocaleMiddleware',
+            'django.middleware.common.CommonMiddleware',
+        ),
+    )
+    def test_backwards_session_language(self):
+        """
+        Check that language is stored in session if missing.
+        """
+        # Create session with old language key name
+        engine = import_module(settings.SESSION_ENGINE)
+        session = engine.SessionStore()
+        session['django_language'] = 'en'
+        session.save()
+        self.client.cookies[settings.SESSION_COOKIE_NAME] = session.session_key
+
+        # request other language; should default to old language key value
+        response = self.client.get('/fr/simple/')
+        self.assertEqual(self.client.session['_language'], 'en')
 
 
 @override_settings(
diff --git a/tests/view_tests/tests/test_i18n.py b/tests/view_tests/tests/test_i18n.py
index 680cd25d6a..777fc24bb1 100644
--- a/tests/view_tests/tests/test_i18n.py
+++ b/tests/view_tests/tests/test_i18n.py
@@ -34,7 +34,7 @@ class I18NTests(TestCase):
             post_data = dict(language=lang_code, next='/views/')
             response = self.client.post('/views/i18n/setlang/', data=post_data)
             self.assertRedirects(response, 'http://testserver/views/')
-            self.assertEqual(self.client.session['django_language'], lang_code)
+            self.assertEqual(self.client.session['_language'], lang_code)
 
     def test_setlang_unsafe_next(self):
         """
@@ -45,7 +45,7 @@ class I18NTests(TestCase):
         post_data = dict(language=lang_code, next='//unsafe/redirection/')
         response = self.client.post('/views/i18n/setlang/', data=post_data)
         self.assertEqual(response.url, 'http://testserver/')
-        self.assertEqual(self.client.session['django_language'], lang_code)
+        self.assertEqual(self.client.session['_language'], lang_code)
 
     def test_setlang_reversal(self):
         self.assertEqual(reverse('set_language'), '/views/i18n/setlang/')