src/transformers/models/marian/tokenization_marian.py/MarianTokenizer/convert_tokens_to_string
class MarianTokenizer:    def convert_tokens_to_string(self, tokens: List[str]) -> str:
        """Uses source spm if _decode_use_source_tokenizer is True, and target spm otherwise"""
        if self._decode_use_source_tokenizer:
            return self.spm_source.DecodePieces(tokens)
        else:
            return self.spm_target.DecodePieces(tokens)