Fake Nationality: While Mulan, Shang and Chi-Fu = Chinese-Americans, Mushu = African-American; Shan Yu = Irish-Puerto Rican; Chien-Po, Ling, the head Ancestor, and the Emperor = Japanese-Americans; Yao = Jewish-American; Mulan's singing voice = Filipina; Shang's singing voice = Osmond-American; Fa Zhou = Korean-American. On the other hand, they're mostly using American Accents.
Non-Singing Voice: B.D. Wong does the speaking voice of Shang but the singing voice — that is, for "I'll Make a Man Out of You" — would be none other than Donny Osmond. (This in spite of Wong being a Broadway performer with a good singing voice. The Word of God on this is that Donny Osmond's singing voice sounds more like B.D. Wong's speaking voice than his own). Ming Na also does Mulan's speaking voice, while her singing is provided by Lea Salonga (who also sang for Princess Jasmine).