You mean like the Norwegians, Swedes, and Finns in Minnesota, Wisconsin, and Michigan's Upper Peninsula? Because they weren't entirely homogenous, they just attracted larger numbers from those countries. Without Cornish immigrants also looking for mining work migrating to the region the pasty would never been introduced and become such a common dish in the region. There were also a lot of other people from within the U.S. moving to the region not to mine, but to set up shops and services for the miners and their families. That would seem to dictate a requirement to learn a common language with English being the favorite choice. Back home for me in the Upper Peninsula there are very few people who still speak Finnish and it is mostly the older folks like my grandfather, a second generation immigrant, who either knew it as a child and was forced to learn and speak English while in school and eventually forgot how to speak Finnish or chose not to pass it on to their children for whatever reason.

But I would like to see a more formal response to your question and could see parallels (maybe) with the Dutch in New York or even the French in Louisiana.