You are not required to speak Chinese when dealing with Chinese manufacturers because it’s them who are trying to sell you stuffs. When you are trying to sell them your designs, that will be the time when you need to speak their language.
Language is the main key to understanding a culture. To learn a language, you cannot do it by textbook or remotely. You have to find ways to understand the culture or else the language will never make sense to you. Therefore, in order to design for the “largest market in the world”, you gotta learn the language.