Fixed #18419 -- Full backwards compatibility for old language codes

Improved documentation about zh-* deprecation and upgrade path.

Thanks to Baptiste Mispelon for the code reviews.

django/utils/translation/trans_real.py

@@ -48,6 +48,12 @@
 
 language_code_prefix_re = re.compile(r'^/([\w-]+)(/|$)')
 
+# some browsers use deprecated locales. refs #18419
+_DEPRECATED_LOCALES = {
+    'zh-cn': 'zh-hans',
+    'zh-tw': 'zh-hant',
+}
+
 
 @receiver(setting_changed)
 def reset_cache(**kwargs):
@@ -202,17 +208,11 @@ def activate(language):
     language and installs it as the current translation object for the current
     thread.
     """
-    if isinstance(language, six.string_types):
-        if language == 'zh-cn':
-            warnings.warn(
-                "The use of the language code 'zh-cn' is deprecated. "
-                "Please use the 'zh-hans' translation instead.",
-                PendingDeprecationWarning, stacklevel=2)
-        elif language == 'zh-tw':
-            warnings.warn(
-                "The use of the language code 'zh-tw' is deprecated. "
-                "Please use the 'zh-hant' translation instead.",
-                PendingDeprecationWarning, stacklevel=2)
+    if language in _DEPRECATED_LOCALES:
+        msg = ("The use of the language code %r is deprecated. "
+               "Please use the %r translation instead.")
+        warnings.warn(msg % (language, _DEPRECATED_LOCALES[language]),
+                      PendingDeprecationWarning, stacklevel=2)
     _active.value = translation(language)
 
 
@@ -410,16 +410,14 @@ def get_supported_language_variant(lang_code, supported=None, strict=False):
     If `strict` is False (the default), the function will look for an alternative
     country-specific variant when the currently checked is not found.
     """
-    # some browsers use deprecated language codes -- #18419
-    if lang_code == 'zh-cn' and 'zh-hans' in supported:
-        return 'zh-hans'
-    elif lang_code == 'zh-tw' and 'zh-hant' in supported:
-        return 'zh-hant'
-
     if supported is None:
         from django.conf import settings
         supported = OrderedDict(settings.LANGUAGES)
     if lang_code:
+        # some browsers use deprecated language codes -- #18419
+        if (lang_code not in supported and lang_code in _DEPRECATED_LOCALES and
+                _DEPRECATED_LOCALES[lang_code] in supported):
+            return _DEPRECATED_LOCALES[lang_code]
         # if fr-CA is not supported, try fr-ca; if that fails, fallback to fr.
         generic_lang_code = lang_code.split('-')[0]
         variants = (lang_code, lang_code.lower(), generic_lang_code,

docs/internals/deprecation.txt

@@ -476,8 +476,8 @@ these changes.
 
 * The class ``django.utils.datastructures.MergeDict`` will be removed.
 
-* The ``zh_CN`` and ``zh_TW`` language codes will be removed and have been
-  replaced by the ``zh_Hans`` and ``zh_Hant`` language code respectively.
+* The ``zh-cn`` and ``zh-tw`` language codes will be removed and have been
+  replaced by the ``zh-hans`` and ``zh-hant`` language code respectively.
 
 2.0
 ---

docs/releases/1.7.txt

@@ -707,10 +707,12 @@ arguments into a ``REQUEST`` property on ``WSGIRequest``. To merge
 dictionaries, use ``dict.update()`` instead. The class ``MergeDict`` is
 deprecated and will be removed in Django 1.9.
 
-Language codes ``zh_CN`` and ``zh_TW``
+Language codes ``zh-cn`` and ``zh-tw``
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-The currently used language codes for Simplified Chinese ``zh_CN`` and
-Traditional Chinese ``zh_TW`` are deprecated and should be replaced by the
-recently introduced language codes ``zh_Hans`` and ``zh_Hant`` respectively.
-The deprecated language codes will be removed in Django 1.9.
+The currently used language codes for Simplified Chinese ``zh-cn`` and
+Traditional Chinese ``zh-tw`` are deprecated and should be replaced by the
+recently introduced language codes ``zh-hans`` and ``zh-hant`` respectively.
+If you use these language codes, you should rename the locale directories
+and update your settings to reflect these changes. The deprecated language
+codes will be removed in Django 1.9.

tests/i18n/tests.py

@@ -893,9 +893,36 @@ def test_support_for_deprecated_chinese_language_codes(self):
         r.COOKIES = {}
         r.META = {'HTTP_ACCEPT_LANGUAGE': 'zh-cn,en'}
         self.assertEqual(g(r), 'zh-hans')
+
         r.META = {'HTTP_ACCEPT_LANGUAGE': 'zh-tw,en'}
         self.assertEqual(g(r), 'zh-hant')
 
+    @override_settings(
+        LANGUAGES=(
+            ('en', 'English'),
+            ('zh-cn', 'Simplified Chinese'),
+            ('zh-hans', 'Simplified Chinese'),
+            ('zh-hant', 'Traditional Chinese'),
+            ('zh-tw', 'Traditional Chinese'),
+        )
+    )
+    def test_backwards_compatibility(self):
+        """
+        While the old chinese language codes are being deprecated, they should
+        still work as before the new language codes were introduced.
+
+        refs #18419 -- this is explicitly for backwards compatibility and
+        should be removed in Django 1.9
+        """
+        g = get_language_from_request
+        r = self.rf.get('/')
+        r.COOKIES = {}
+        r.META = {'HTTP_ACCEPT_LANGUAGE': 'zh-cn,en'}
+        self.assertEqual(g(r), 'zh-cn')
+
+        r.META = {'HTTP_ACCEPT_LANGUAGE': 'zh-tw,en'}
+        self.assertEqual(g(r), 'zh-tw')
+
     def test_parse_language_cookie(self):
         """
         Now test that we parse language preferences stored in a cookie correctly.