People speaking a language is not a useful way of choosing your borders. Otherwise most of Latin America can revert to Spanish control, the US can be annexed by the UK, countries like Morocco can be colonies of the French again. The fact is that spreading your language is a basic element of empire building. The fact that Crimea, Ukraine etc have so many Russian speakers reflects their past.

I think what GP meant is that majority of people in Crimea self-identify as Russians, not Ukrainians - 68%, according to Wikipedia [1]

Similar thing can be said about disputed teritorries in the east, around Donbas.

Of course that's still not the excuse for what Russia did, taking both places by force, however, this makes fixing this more complicated.

[1] https://en.wikipedia.org/wiki/Crimea#Demographics

Ethically identifying as Russian is certainly not equivalent to identifying as a Russian.

So, people speak English many places and the UK doesn't have any right to control those areas.

Look at the context (Crimea, 2020). If we are choosing between ancient greeks and russians then the language/culture/identity of the people should matter.

This is not about Ancient Greece/Rome/Russia/etc. My comment was: you cannot cherry pick which moment in History, a country's borders are convenient to you. I remember talking to a colleague from Poland that was proud that X centuries ago, Poland (or whatever the country/nation was called at the time had conquered big parts of then-Russia, even conquered Moscow. If we all think like that then a WW3 (Romans, Nazis, Mongols, etc.) is certain.

Let's stick to the borders we got, and in the future let's rener them useless (e.g. European Union).

I believe in a Star Trek society. Not "we kicked butts back then so let's get back those lands".

According to you, the East and West Germany shouldn't have merged to "stick to the borders we got"