src/transformers/models/marian/tokenization_marian.py/MarianTokenizer/save_vocabulary
class MarianTokenizer:    def save_vocabulary(self, save_directory: str, filename_prefix: Optional[str] = None) -> Tuple[str]:
        save_dir = Path(save_directory)
        assert save_dir.is_dir(), f"{save_directory} should be a directory"
        save_json(
            self.encoder,
            save_dir / ((filename_prefix + "-" if filename_prefix else "") + self.vocab_files_names["vocab"]),
        )

        for orig, f in zip(["source.spm", "target.spm"], self.spm_files):
            dest_path = save_dir / ((filename_prefix + "-" if filename_prefix else "") + Path(f).name)
            if not dest_path.exists():
                copyfile(f, save_dir / orig)

        return tuple(
            save_dir / ((filename_prefix + "-" if filename_prefix else "") + f) for f in self.vocab_files_names
        )