    def add_args(parser):
        """Add task-specific arguments to the parser."""
        # fmt: off
        TranslationTask.add_args(parser)
        parser.add_argument('--langs',  type=str, metavar='LANG',
                            help='comma-separated list of monolingual language, '
                                 'for example, "en,de,fr". These should match the '
                                 'langs from pretraining (and be in the same order). '
                                 'You should always add all pretraining language idx '
                                 'during finetuning.')
        parser.add_argument('--prepend-bos', action='store_true',
                            help='prepend bos token to each sentence, which matches '
                                 'mBART pretraining')
Add task-specific arguments to the parser.
fairseq/tasks/translation_from_pretrained_bart.py