src/transformers/models/plbart/tokenization_plbart.py/PLBartTokenizer/vocab_size
class PLBartTokenizer:    def vocab_size(self):
        if self.language_codes == "base":
            return (
                len(self.sp_model) + len(self.lang_code_to_id) + self.fairseq_offset + 1
            )  # Plus 1 for the mask token
        else:
            return len(self.sp_model) + len(self.lang_code_to_id) + self.fairseq_offset