Context dependent. When you use a general word in one language, there is often no general word in the other language. The more context you can give, the more likely you are to get a fitting response. What sort of 合作? Looking forward to our next .... Looking forward to the next time we can .... Looking forward to the next time we can cooperate. Looking forward to the next time we can do business. Looking forward to our next business venture. Looking forward to our next endevour. Looking forward to our next escapade. Looking forward to our next adventure.