APAD：入乡随俗 英文谚语怎么说？先想想再看进来：

When in Rome means that you should adopt the customs and practices of the place you are visiting. The proverb is an abbreviation of the longer expression When in Rome, do as the Romans do. But you can get away with just saying the first part and people will still understand, nod knowingly, and deem you a person of learning and culture.