Speaking of language boundaries… There are numerous dialects all over place that are organically meshed together along borders.

Czech and Moravian dialects are rather close, with some pockets that have a unique character. Specifically Brno has a special dialect called Hantec (pron. hantets) that is not static and evolving all the time. It uses a lot of neologisms, a bit of czechized German and syntactical or structural constructs that are unintelligible to speakers from other parts of Czech Republic.

Czech and Slovak are mutually highly intelligible. Polish and Czech less so, but after some adjustments, you can carry conversation with little problem. Slovak may be a tiny bit more Intelligible to a Polish speaker. In eastern Slovakia, there is a lot of Rusins that speak a western version of an Ukrainian dialect. Still a high degree of commonality between Czech and Rusin. Further east you go, the more Russian influence you find and you encounter substantial shifts in meaning of words and words that are unknown.

You can see a similar continuity between Polish and Ukrainian dialects.

Similar pattern is present when you go south. Slovinian is fairly intelligible to a Czech or Slovak, although some hilarity may ensue–usually one can bridge it by reverting to more archaic word forms. Serbo-Croatian is a bit tougher, but a half dozen days and you get the gist of it. More south and east, Bulgarian dialects have a bit more common with Russian, but somewhat unique syntax. Give me 10 days and I’d be able to cover basics.

But, perhaps that’s me. During my stay in Italy, I was able to communicate fairly well in Italian at the time of my departure to Canada. Not much left of it, use it or lose it.