Miranda Wilkerson (a recent Wisconsin Ph.D. who does second language acquisition) and our contributor Joe just had a piece in American Speech showing that German-speaking immigrants to Wisconsin didn't learn English quickly, in fact even for two or three generations in many cases. It's called "'Good old immigrants of yesteryear' who didn't learn English" and appears in vol. 83, pp. 259-283. They note that scholars like Calvin Veltman show that contemporary immigrants, in contrast, are learning English as fast as they can.
The local paper has picked up the story, here. The 'community comments' section after on-line articles is pretty consistently a forum for screaming wingnuts. It's kinda of like a Palin rally in cyberspace in terms of the attitude toward the media and the racism. It's interesting in this case that a lot of people are actually speaking up showing some knowledge of family, local and state history.