>Did he consult mongolia and ask for the right to use their art and culture? Or did he steal the idea and give nothing back?
I've seen a few people taking this line in the comments, and I find it really confusing. The Mongolian government of the day is not necessarily the arbiter of their culture. There are many cases of a government actively trying to stamp out cultures. No such body exists that can approve cultural elements in films.
Now I think it's pretty safe to assume that George Lucas didn't consult anyone from Mongolia or involved in Mongolian culture, or really give a shit about the costume at all except that he thought it looked cool and, to his eyes, unusual.
But I would expect that a world-class costume designer like Trisha Biggar is an expert on world culture, especially as it relates to their clothing, and did extensive research and consulting in designing the costumes. I haven't read her book on the topic since, you know, it's a $300 book about the prequels, but I bet it's enlightening.
They made a book of it.
http://www.amazon.com/Dressing-Galaxy-Costumes-Star-Wars/dp/0810965674