src/transformers/models/marian/convert_marian_to_pytorch.py/OpusState/load_tokenizer
class OpusState:    def load_tokenizer(self):
        # save tokenizer
        add_special_tokens_to_vocab(self.source_dir, not self.share_encoder_decoder_embeddings)
        return MarianTokenizer.from_pretrained(str(self.source_dir))