Does everyone in Firefly fully speak Chinese or just know Chinese slang?

Often the English-speaking characters in Firefly speak curses and slang in Chinese because of the mixing of American and Chinese cultures in the universe. Often audio recordings are also said in both English and Chinese.

I am wondering if there is any canon source that says that the English-speaking characters such as the Serenity crew actually know Chinese or if they simply know Chinese curses and slang.