Konyok said:

“If one were to draw a line from Rostov to Krakow a smooth linguistic continuum would be revealed. There are no sharp lines; Russian grades into Ukrainian which grades into Polish…”

This is true for all of Europe. I don’t speak Russian but know (or knew) a little German. Get on the train in Hannover and almost everyone is speaking Hochdeutsch (high German). As the train goes east, the original Hanover passengers get off and locals climb on board speaking their local dialect (Plattdeutsch). The dialect gets more and more rustic as the train goes west. Eventually, I can’t understand what anyone is saying as the train approaches the border between Germany and the Netherlands (almost everyone is speaking Dutch). Riding European trains is a great way to experience the local dialects.