Fixed #27868 -- Filtered locale path subdirectories

Thanks Tim Graham for the review.

django/core/management/commands/makemessages.py

@@ -337,8 +337,12 @@ class Command(BaseCommand):
                     os.makedirs(self.default_locale_path)
 
         # Build locale list
+        looks_like_locale = re.compile(r'[a-z]{2}')
         locale_dirs = filter(os.path.isdir, glob.glob('%s/*' % self.default_locale_path))
-        all_locales = map(os.path.basename, locale_dirs)
+        all_locales = [
+            lang_code for lang_code in map(os.path.basename, locale_dirs)
+            if looks_like_locale.match(lang_code)
+        ]
 
         # Account for excluded locales
         if process_all:

tests/i18n/test_extraction.py

@@ -604,6 +604,7 @@ class KeepPotFileExtractorTests(ExtractorTests):
 class MultipleLocaleExtractionTests(ExtractorTests):
     PO_FILE_PT = 'locale/pt/LC_MESSAGES/django.po'
     PO_FILE_DE = 'locale/de/LC_MESSAGES/django.po'
+    PO_FILE_KO = 'locale/ko/LC_MESSAGES/django.po'
     LOCALES = ['pt', 'de', 'ch']
 
     def test_multiple_locales(self):
@@ -611,6 +612,18 @@ class MultipleLocaleExtractionTests(ExtractorTests):
         self.assertTrue(os.path.exists(self.PO_FILE_PT))
         self.assertTrue(os.path.exists(self.PO_FILE_DE))
 
+    def test_all_locales(self):
+        """
+        When the `locale` flag is absent, all dirs from the parent locale dir
+        are considered as language directories, except if the directory doesn't
+        start with two letters (which excludes __pycache__, .gitignore, etc.).
+        """
+        os.mkdir(os.path.join('locale', '_do_not_pick'))
+        # Excluding locales that do not compile
+        management.call_command('makemessages', exclude=['ja', 'es_AR'], verbosity=0)
+        self.assertTrue(os.path.exists(self.PO_FILE_KO))
+        self.assertFalse(os.path.exists('locale/_do_not_pick/LC_MESSAGES/django.po'))
+
 
 class ExcludedLocaleExtractionTests(ExtractorTests):