Fixed #18430 -- Use the FILE_CHARSET setting when reading from a file during post processing with the cached staticfiles storage. Thanks to Brant Young for initial debugging.

django/contrib/staticfiles/storage.py

@@ -228,7 +228,7 @@ class CachedFilesMixin(object):
 
                 # ..to apply each replacement pattern to the content
                 if name in adjustable_paths:
-                    content = original_file.read()
+                    content = original_file.read().decode(settings.FILE_CHARSET)
                     converter = self.url_converter(name)
                     for patterns in self._patterns.values():
                         for pattern in patterns:

tests/regressiontests/staticfiles_tests/apps/test/static/test/nonascii.css

@@ -0,0 +1,5 @@
+body {
+  background: url('window.png');
+}
+
+.snowman:before { content: "☃"; }

tests/regressiontests/staticfiles_tests/tests.py

@@ -498,8 +498,9 @@ class TestCollectionCachedStorage(BaseCollectionTestCase,
         collectstatic_cmd = CollectstaticCommand()
         collectstatic_cmd.set_options(**collectstatic_args)
         stats = collectstatic_cmd.collect()
-        self.assertTrue(os.path.join('cached', 'css', 'window.css') in stats['post_processed'])
-        self.assertTrue(os.path.join('cached', 'css', 'img', 'window.png') in stats['unmodified'])
+        self.assertIn(os.path.join('cached', 'css', 'window.css'), stats['post_processed'])
+        self.assertIn(os.path.join('cached', 'css', 'img', 'window.png'), stats['unmodified'])
+        self.assertIn(os.path.join('test', 'nonascii.css'), stats['post_processed'])
 
     def test_cache_key_memcache_validation(self):
         """