have a good command of a language如不明白请追问，如果满意请采纳手机提问者如果满意，请在客户端右上角评价点“满意”即可， 谢谢！祝学习进步
mastery of a language
Being good at a kind of language;哥这才是标准答案！！
Proficient in a language望采纳！！！
