locale.setlocale() does not work if you pass it a ``unicode`` object instead of a ``str`` (locale.py, line 576):

    ``if locale and type(locale) is not type(""):``

Maybe it would be better to do a check like this?

    ``if locale and not isinstance(locale, basestring):``

In particular, this can bite you if you use the ``unicode_literals`` future import, displaying a not-so-helpful error message ("ValueError: too many values to unpack" in _build_localename).