From Lingo: Around Europe in Sixty Languages, by Gaston Dorren (Atlantic Monthly Press, 2015), Kindle Loc. 2006-26:
Whether they’re from the Baltic port of Kaliningrad or from Vladivostok on the Sea of Japan, there’s little difference in the way Russians speak. In Poland, the same holds true: North Poles and South Poles can chat away effortlessly to each other, as can West and East Poles. Even people speaking different Slavic languages can often communicate without much trouble. Bulgarians can converse with Macedonians, Czechs with Slovaks, and Russians with Belarusians and Ukrainians. And, for all their political differences, there is no great language barrier between Croats, Bosnians, Serbs and Montenegrins. In fact, as the eminent nineteenth-century Slovak scholar Ján Kollár suggested, the Slavic world could, with no great effort on the part of its citizens, adopt just four standard languages: Russian, Polish, Czechoslovak and, lastly, what you might call Yugoslav or South Slavic.
There is one language, however, that wouldn’t so easily be absorbed into Kollár’s scheme: Slovene, also known as Slovenian. Admittedly, this is the language of a very small nation. Its entire territory fits no fewer than twelve times into the area of the UK (which is itself not large) and the population, at just over two million, is just a quarter of that of London. And yet, when Slovenes speak their local dialects, many of their compatriots can make neither head nor tail of what they are saying. So just imagine how these dialects would bewilder the members of some of the other nations that Kollár lumped together as ‘South Slavic’, such as the Bulgarians.
How come? Why does Russian span more than four thousand miles from west to east with next to nothing in the way of dialect diversity, whereas the Slovene language area, measuring just two hundred miles from end to end, is a veritable smorgasbord of regional varieties? Which in turn raises the question: how do dialects come about in the first place?
One school of thought, or rather thoughtlessness, holds that dialects are corrupted forms of the standard language – as, for example, in the view that ‘Scouse is just bad English’. This might be one’s automatic reaction, but it’s in fact the wrong way round: dialects come first, and tend to be at the root of any standard language, which is always an artefact. It would be nearer the truth to claim that standards are ‘corrupted’, ‘unnatural’ or ‘perverted’ dialects. For any other variation of any language, regional or otherwise, develops in a largely unselfconscious way, influenced chiefly by its degree of isolation and contact.