You could make translit a subparser/subcommand which would work as prog translit -h
or just prog translit
which if there are needed options missing, would display the help text.
Something along the lines of
parser = argparse.ArgumentParser()
parser.add_argument('-s', '--string', required=True)
subparsers = parser.add_subparsers(dest='subcommand_name')
translit_parser = subparsers.add_parser('translit')
translit_parser.add_argument('x', required=True)
parser.parse_args()
python test.py translit
would output something like:
usage: test.py translit [-h] -x X
test.py translit: error: argument -x is required