I have been asked to perform a marriage between an caucasian American
who speaks Chinese and a Chinese who speaks no English and has never
been to the US. Both are 22 and atheists. I speak no Chinese and am
not particularly good at pronouncing forgein words. I want it to be a
meaningful but short ceremony. Any advice? Art

Have you considered performing the ceremony in a language other than
English or Chinese? A short ceremony in Esperanto or American Sign
Language would not be difficult to learn, and it would be memorably
unusual for both the couple and the guests.

I love your question.  It sounds like a bind I would find myslef in. 
There is nothing special about my solution, but I'm fairly certain I
would find an inturpreter, because it's important that they get a
clear understanding of the commitment they are making.  Good luck.