The following code in optparse:

            if len(rargs) < nargs:
                if nargs == 1:
                    self.error(_("%s option requires an argument") % opt)
                else:
                    self.error(_("%s option requires %d arguments")
                               % (opt, nargs))

works for languages with plurals of n!=1 but will not work for many
others that have more sophisticated plurals.

I've created a patch that handles missing gettext and implements it
correctly if it is available. Be aware that I have not been able to test
the patch.