挥汗成雨的英文是「wiping off their sweat drops makes it look like rain」
hui han cheng yu
挥:洒,泼。用手抹汗,汗洒下去就跟下雨一样。形容人多。
《战国策·齐策一》:“连衽成帷,举袂成幕,挥汗成雨。”