Enforcement Rules for the Attorney Regulation Act Article 27
A foreign legal affairs attorney shall perform his or her duties in and present documents to a court or a prosecutors office in the official language of the Republic of China (i.e., Mandarin).
中文原文 律師法施行細則第27條
外國法事務律師於法院或檢察署執行職務時，應用中華民國國語；所陳文件，應用中華民國文字。