src/transformers/models/marian/convert_marian_to_pytorch.py/save_tokenizer_config
def save_tokenizer_config(dest_dir: Path):
    dname = dest_dir.name.split("-")
    dct = dict(target_lang=dname[-1], source_lang="-".join(dname[:-1]))
    save_json(dct, dest_dir / "tokenizer_config.json")