他让我明天替王东给旅行团当翻译 He asked me to do Wang Dong's translation job for the group tomorrow. If A 替 B do something, then A does or will do that thing instead of B because B is not available or because of some other unexpected stuff. 给 here means for (do something for someone/organization, or work for someone or an organization)

Thanks so much all

他让我明天替王东给旅行团当翻译 He asked me to do Wang Dong's translation job for the group tomorrow. To 替 someone do something is to do that thing because that person is not available or because of some other unexpected things. 给 here means for (do something for someone/organization, or work for someone or an organization)

用replace并不好，这暗示我取代了王东，或者王东的位置原来是，现在我又重新回到这个位置上。用instead of, in place of, on one's behalf of勉强能和这里的“替”的意思相当。

他 让 我 明天 替 王东 给 旅行团 当 翻译 He will let me tomorrow substitute Wang Dong for tourism group become translator Tomorrow he will let me substitute Wang Dong as a guide for a group of tourists.