'user_lang()
Fetches the res.lang record corresponding to the language code stored
in the user\'s context. Fallbacks to en_US if no lang is present in the
context *or the language code is not valid*.
:returns: res.lang browse_record'

@api.model
def user_lang(self):

    lang_code = (self._context.get('lang') or 'en_US')
    return self.env['res.lang']._lang_get(lang_code)
