One thing that strikes me often enough is that most of the major planets in the ST universe, Vulcan, Kronos, Romulus, Cardassia, Bajor etc are all unified to the point where there are no countries and usually a shared language. The one exception is Earth (I think) which still have countries altough it seems that they are all more or less adapted to a western european cultural hegemony.
So are there any examples where a planet actually have countries with different cultures, it seems to be impossible for a whole planet to have one culture and one language in real life, but in Star Trek there are several. Would be very refreshing with a Vulcan who comes from some other culture then Spocks, but yeah, would be hard for the show to implement.
Actually the idea of one language emerging is not too far fetched, because this century thousands of languages are likely to become extinct, as literacy and standardization whittle many tribal languages down to a few national ones, like Spanish, Mandarin, English, etc.
Linguistic mono-cultures are not as unrealistic as they seem - and probably Vulcan, Kronos, etc, only superficially seem like mono-cultures - Bajor seemed to have many regions - probably as different from one another as our major countries. But differences can seem more and more minor when in a planetary union - like within the European Union, there is hardly any difference between the lifestyle of a German and French citizen - but only 70 years ago, they were at war. Maybe people in those Bajoran uniforms are similar; we just don't hear them talk about national differences.
We have little evidence for how the Federation is actually run, probably by design, to keep it from getting outdated when some real historical events actually happen. But judging by how Andoria has something called an Imperial Guard, and Vulcan has it's own traditions, the British flag can be seen on some buildings on Earth, etc, I recon that perhaps the Federation is a natural hodge-podge of development resulting in union of worlds with similar levels of humanoid rights, just like real life Earth has a hodge podge of overlapping treaties and differing engagement that trend toward more peace. As opposed to a centralized republic that forced standardization on United Earth and Vulcan.
Maybe events like Brexit can actually still happen in the Federation - we simply don't know what planetary politics is like - just imagine that it is much more of an academic thing when this happens, since being a post-scarcity society, people don't actually die from depression and unemployment, if say Britain chooses to exit the United Federation of Planets for some obscure national/local reason for a few decades, such as objection to changes in the school curriculum or something (I dunno, I'm just making it up, I dunno what would get people riled in a post-scarcity society).
