Back to the PT, In TPM there are three alien species that have accents, and only Huttese is spoken as the foreign language within the movie. By AOTC, there is some Geonosian, and by ROTS there is little or no foreign language. So there arent enogh species in the entire PT to justify using (presumably ethnic) accents.
It is interesting to note that Han never speaks aforeign language, but only interprets it.