src/transformers/models/plbart/tokenization_plbart.py/PLBartTokenizer/_convert_lang_code_special_format
class PLBartTokenizer:    def _convert_lang_code_special_format(self, lang: str) -> str:
        """Convert Language Codes to format tokenizer uses if required"""
        lang = FAIRSEQ_LANGUAGE_CODES_MAP[lang] if lang in FAIRSEQ_LANGUAGE_CODES_MAP.keys() else lang
        return lang