There's a similar thing in Germany.
In Saxony, there's a region where Serbs(they're not from Serbia) live, they're called "Sorben". They're slavs but live in Germany since the middle ages, some of younger ones don't speak their language anymore, but many of the older ones do. They even have special schools where they don't teach German but their slavic language.
It's funny, I can understand like 60% cuz it's a mix of Czech, Polish and Russian. I don't know any Czech but I know the other two.