Decode from UTF-8 explicitly when reading a text file in makemessages.

This shows itself with Python 3 under Windows where UTF-8 usually isn't
the default file I/O encoding and caused one failure and three errors
in our test suite under that platform setup.

django/core/management/commands/makemessages.py

 import fnmatch
 import glob
+import io
 import os
 import re
 import sys
@@ -10,6 +11,7 @@ import django
 from django.core.management.base import CommandError, NoArgsCommand
 from django.core.management.utils import (handle_extensions, find_command,
     popen_wrapper)
+from django.utils.encoding import force_str
 from django.utils.functional import total_ordering
 from django.utils.text import get_text_list
 from django.utils.jslex import prepare_js_for_gettext
@@ -402,16 +404,17 @@ class Command(NoArgsCommand):
         for domain in domains:
             django_po = os.path.join(django_dir, 'conf', 'locale', locale, 'LC_MESSAGES', '%s.po' % domain)
             if os.path.exists(django_po):
-                with open(django_po, 'rU') as fp:
+                with io.open(django_po, 'rU', encoding='utf-8') as fp:
                     m = plural_forms_re.search(fp.read())
                 if m:
+                    plural_form_line = force_str(m.group('value'))
                     if self.verbosity > 1:
-                        self.stdout.write("copying plural forms: %s\n" % m.group('value'))
+                        self.stdout.write("copying plural forms: %s\n" % plural_form_line)
                     lines = []
                     found = False
                     for line in msgs.split('\n'):
                         if not found and (not line or plural_forms_re.search(line)):
-                            line = '%s\n' % m.group('value')
+                            line = '%s\n' % plural_form_line
                             found = True
                         lines.append(line)
                     msgs = '\n'.join(lines)

tests/i18n/commands/extraction.py

 # -*- encoding: utf-8 -*-
 from __future__ import unicode_literals
 
+import io
 import os
 import re
 import shutil
@@ -65,8 +66,8 @@ class BasicExtractorTests(ExtractorTests):
         os.chdir(self.test_dir)
         management.call_command('makemessages', locale=LOCALE, verbosity=0)
         self.assertTrue(os.path.exists(self.PO_FILE))
-        with open(self.PO_FILE, 'r') as fp:
-            po_contents = force_text(fp.read())
+        with io.open(self.PO_FILE, 'r', encoding='utf-8') as fp:
+            po_contents = fp.read()
             self.assertTrue('#. Translators: This comment should be extracted' in po_contents)
             self.assertTrue('This comment should not be extracted' not in po_contents)
             # Comments in templates
@@ -363,8 +364,8 @@ class CopyPluralFormsExtractorTests(ExtractorTests):
         os.chdir(self.test_dir)
         management.call_command('makemessages', locale='es', extensions=['djtpl'], verbosity=0)
         self.assertTrue(os.path.exists(self.PO_FILE_ES))
-        with open(self.PO_FILE_ES, 'r') as fp:
-            po_contents = force_text(fp.read())
+        with io.open(self.PO_FILE_ES, 'r', encoding='utf-8') as fp:
+            po_contents = fp.read()
             found = re.findall(r'^(?P<value>"Plural-Forms.+?\\n")\s*$', po_contents, re.MULTILINE | re.DOTALL)
             self.assertEqual(1, len(found))