keep a civil tongue
意思是：别那么粗鲁！要讲礼貌！
也就是劝人注意用语，说话文明点
避免使用无礼或粗鲁的语言
举个例子：
I don't want any outbursts between you and your sister during this dinner, so please keep a civil tongue, understood?
我不希望你和你妹妹在晚餐期间发生任何争吵，所以讲话客气点，明白吗?
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