This issue seems already fixed.

File: Lib/argparse.py
922         # if we didn't use all the Positional objects, there were too few
1923         # arg strings supplied.
1924         if positionals:
1925             self.error(_('too few arguments'))
1926 
1927         # make sure all required actions were present
1928         for action in self._actions:
1929             if action.required:
1930                 if action not in seen_actions:
1931                     name = _get_action_name(action)
1932                     self.error(_('argument %s is required') % name)