#i can't speak for the rest of asia/other countries and languages that are outside the sinic cultural sphere

[possamble]

if you're ever wondering why some japanese fantasy media with meticulous worldbuilding randomly has like normal-ass months and dates. it's bc calendar months being named after specific myths or historical figures is not a thing in east asian languages, all months are just called month 1, month 2, month 3, etc. so setting a normal date based on a 12-month calendar doesn't actually seem incongruous with fantasy

[max1461]

What’s the deal with Basque. It’s a language isolate but are the Basque people like an “ethnic isolate”? Are the Basque people significantly genetically different than neighboring peoples? Is there any particular reason everyone else in Europe was either exterminated or assimilated by the Indo-Europeans, at least to the point that they adopted IE languages—but not the Basques?

Regarding genetics, I can't really say. Genetics is way outside my area of expertise, and looking online it doesn't appear that there's a real consensus. It appears that the general picture is that they have some amount of local hunter-gatherer ancestry and some amount of admixture from steppe populations, which is qualitatively the same as the rest of Europe. They may have these things in different proportions(?) than other European populations, or something like that; it sounds like a number of the studies disagree with each other. I think I'd have to have a better understanding of human genetics in general to give a more confident assessment of what is going on.

Linguistically speaking, Basque is the only non-IE language spoken in Western Europe today (Uralic languages, such as Finnish and Hungarian, are spoken in Eastern Europe, although they are probably later arrivals to the region than even IE), but it is not the only non-IE spoken in Western Europe within recorded history. The collective name for the languages spoken in the Iberian peninsula before the Roman conquest is the paleo-Iberian or Paleohispanic languages; of these, several were not Indo-European. Aquitanian in particular is generally identified as a direct ancestor of Basque. But there were also others, scantily attested, that may or may not have been related. These existed alongside Continental Celtic languages in the region.

There was also Etruscan, in Italy, which was non-IE. Etruscan civilization largely predated the Romans in the area and was highly influential on them; the Latin alphabet is principally adapted from the Etruscan alphabet (itself adapted from Greek), and Latin borrowed a number of words from Etruscan. Some of these have even made their way into English, for instance the very common word person, from Latin persōna "mask", possibly from Etruscan phersu "mask".

Anyway, whether or not any of these languages represent holdovers of the pre-IE linguistic environment in Europe is hard to say. For instance, some have argued that the Etruscans or their ancestors were actually late arrivals from somewhere south, possibly Anatolia. But I don't think there is any conclusive evidence for or against such ideas.

It is worth noting that ethnic and linguistic groupings very often don't align. Groups may remain ethnically distinct while adopting a majority language, or may remain linguistically distinct while losing a sense of ethnic identity, and so on. So genetic studies are often-useful-but-highly-imperfect proxies for linguistic relatedness, and vice versa. For instance, most of the "Negrito" peoples of South East Asia are highly genetically distinct from neighboring populations, but many of them speak Aslian languages related (distantly) to Vietnamese and Khmer. These languages are clearly distinct, but should not be misunderstood as holdovers predating the spread of genetically East Asian people to the region.

My understanding is that the evidence regarding Basque points to it being as pre-IE holdout in Western Europe. However, this need not say much about the genetics of the Basque people.

In any case, as to the question of "why" it held out when other pre-IE languages disappeared? I think it's kind of impossible to say. Presumably the mountainous and isolated nature of the Basque Country played a role; indeed all the studies I looked at seemed to say that genetically Basque people showed signs of isolation within the last thousand years or so, suggesting that they did not have as much contact with other European populations. But, beyond that, if you look at the fact that other pre-IE (or at least non-IE) languages survived in Western Europe until the historical period (Etruscan and some paleo-Iberian), it is perhaps not so surprising that at least one of them would make it to the modern day. Basque looks like a complete outlier now, but going back even 2000 years and there were a number of other languages in its position. In some sense the Indo-European migration into Europe was "not that long ago", on archeological timescales, so perhaps things like this are to be expected.