Certainly language is a huge barrier to the U.S. melting pot. One day I went to lunch with a group of coworkers who are all Vietnamese. Even though my coworkers were fluent in English, they spoke Vietnamese the entire time. I might as well have sat at a table by myself considering how much I could participate. Growing up in Iowa with Danish Christian values, this behavior would be considered rude.
I'm not sure multiculturalism means we are one big happy family.