diff -r 4c19396bd4a0 Lib/argparse.py
--- a/Lib/argparse.py	Sat Apr 09 14:05:19 2016 +0000
+++ b/Lib/argparse.py	Sat Apr 09 18:39:37 2016 -0400
@@ -721,7 +721,7 @@
         if self.argument_name is None:
             format = '%(message)s'
         else:
-            format = 'argument %(argument_name)s: %(message)s'
+            format = _('argument %(argument_name)s: %(message)s')
         return format % dict(message=self.message,
                              argument_name=self.argument_name)