I've done plenty of ethnic parties, and you don't need to OD on the music of the motherland. Except for the only Orthodox Jewish wedding I ever played (which will be my first AND last!) I have found that most parties respond to a nice mix. I'd suggest having maybe 1 or 2 polkas ready and maybe a few specialty numbers if you are aware of any, but they hired a well rounded, variety entertainer, not a specialty act ... make a nice playlist for break-time and ask the client for any special requests well in advance of the affair. Good luck!