Refactored DjangoTranslation class

Also fixes #18192 and #21055.

AUTHORS

@@ -104,6 +104,7 @@ answer newbie questions, and generally made Django that much better:
     Batman
     Oliver Beattie <oliver@obeattie.com>
     Brian Beck <http://blog.brianbeck.com/>
+    Doug Beck <doug@douglasbeck.com>
     Shannon -jj Behrens <http://jjinux.blogspot.com/>
     Esdras Beleza <linux@esdrasbeleza.com>
     Božidar Benko <bbenko@gmail.com>

tests/i18n/tests.py

@@ -4,6 +4,7 @@ from __future__ import unicode_literals
 from contextlib import contextmanager
 import datetime
 import decimal
+import gettext as gettext_module
 from importlib import import_module
 import os
 import pickle
@@ -1338,3 +1339,26 @@ class CountrySpecificLanguageTests(TestCase):
         r.META = {'HTTP_ACCEPT_LANGUAGE': 'pt-pt,en-US;q=0.8,en;q=0.6,ru;q=0.4'}
         lang = get_language_from_request(r)
         self.assertEqual('pt-br', lang)
+
+
+class TranslationFilesMissing(TestCase):
+
+    def setUp(self):
+        super(TranslationFilesMissing, self).setUp()
+        self.gettext_find_builtin = gettext_module.find
+
+    def tearDown(self):
+        gettext_module.find = self.gettext_find_builtin
+        super(TranslationFilesMissing, self).tearDown()
+
+    def patchGettextFind(self):
+        gettext_module.find = lambda *args, **kw: None
+
+    def test_failure_finding_default_mo_files(self):
+        '''
+        Ensure IOError is raised if the default language is unparseable.
+        Refs: #18192
+        '''
+        self.patchGettextFind()
+        trans_real._translations = {}
+        self.assertRaises(IOError, activate, 'en')