actually, warpath, i'm pretty sure you're considered an international student, not a URM, because i believe you're technically either a canadian or nigerian citizen (i'm not sure which based on your post). the 'african-american' designation, for the sake of applications like this, generally refers to american citizens who are of african heritage.
determining URM status is pretty straightforward. basically, anyone who identifies themselves african-american, native american, mexican-american, or from mainland puerto rican is an underrepresented minority. being 'disadvantaged' is a separate issue. personally i interpreted the question about other languages to either indicate whether you may have had an language obstacle when you first started school (indicating a disadvantage) or if you speak some other language that could potentially be useful as a physician (like spanish).