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.)