Fallback i18n js files for zh-hans/zh-hant. (#468)

* Fallback i18n js files for zh-hans/zh-hant.

* Use Django admin's built-in SELECT2_TRANSLATIONS to determine the lang of i18n js files.

Author: dzhuang

django_select2/forms.py

@@ -98,12 +98,23 @@ def _get_media(self):
         .. Note:: For more information visit
             https://docs.djangoproject.com/en/stable/topics/forms/media/#media-as-a-dynamic-property
         """
+        lang = get_language()
+        i18n_name = None
         try:
-            # get_language() will always return a lower case language code, where some files are named upper case.
-            i = [x.lower() for x in settings.SELECT2_I18N_AVAILABLE_LANGUAGES].index(get_language())
-            i18n_file = ('%s/%s.js' % (settings.SELECT2_I18N_PATH, settings.SELECT2_I18N_AVAILABLE_LANGUAGES[i]), )
-        except ValueError:
-            i18n_file = ()
+            from django.contrib.admin.widgets import SELECT2_TRANSLATIONS
+            i18n_name = SELECT2_TRANSLATIONS.get(lang)
+            if i18n_name not in settings.SELECT2_I18N_AVAILABLE_LANGUAGES:
+                i18n_name = None
+        except ImportError:
+            # TODO: select2 widget feature needs to be backported into Django 1.11
+            try:
+                i = [x.lower() for x in settings.SELECT2_I18N_AVAILABLE_LANGUAGES].index(lang)
+                i18n_name = settings.SELECT2_I18N_AVAILABLE_LANGUAGES[i]
+            except ValueError:
+                pass
+
+        i18n_file = ('%s/%s.js' % (settings.SELECT2_I18N_PATH, i18n_name),) if i18n_name else ()
+
         return forms.Media(
             js=(settings.SELECT2_JS,) + i18n_file + ('django_select2/django_select2.js',),
             css={'screen': (settings.SELECT2_CSS,)}

tests/test_forms.py

@@ -129,13 +129,22 @@ def test_i18n(self):
             'django_select2/django_select2.js'
         )
 
-        translation.activate('zh-cn')
+        pytest.importorskip("django", minversion="2.0.4")
+
+        translation.activate('zh-hans')
         assert tuple(Select2Widget().media._js) == (
             '//cdnjs.cloudflare.com/ajax/libs/select2/4.0.3/js/select2.min.js',
             '//cdnjs.cloudflare.com/ajax/libs/select2/4.0.3/js/i18n/zh-CN.js',
             'django_select2/django_select2.js'
         )
 
+        translation.activate('zh-hant')
+        assert tuple(Select2Widget().media._js) == (
+            '//cdnjs.cloudflare.com/ajax/libs/select2/4.0.3/js/select2.min.js',
+            '//cdnjs.cloudflare.com/ajax/libs/select2/4.0.3/js/i18n/zh-TW.js',
+            'django_select2/django_select2.js'
+        )
+
 
 class TestSelect2MixinSettings(object):
     def test_default_media(self):