Some governments (like El Salvador and Russia) are moving into bitcoin mining. If more nation-states accumulate BTC, what impact will this have on decentralization and price stability? Could this lead to geopolitical bitcoin wars?
Do you have any evidence that the Russian government is investing in BTC mining? I find it hard to believe that the Russian government would invest in Bitcoin mining. The Russian government is currently "investing" in tanks, rockets, weapons and artillery shells.

What impact could this have on the BTC price? It would most likely pump the price, but I find it highly unlikely that the big and developed countries would suddenly start mining Bitcoins.
Geopolitical Bitcoin wars? Are you kidding me? The countries would start wars over rare-earth minerals, oil, gas or water, but they won't start wars over the possession of Bitcoin or any other cryptocurrency.
I think you are right about Russians about their lifestyle and what they know how to do very well but that doesn't mean that the government can not invest in Bitcoin, Russia is one of the strong countries that value weapons because they always take war very serious but having an interest in Bitcoin is not bad, no matter hard a country is there are still some things that will draw the country attention to do it, and from my observation, there is no any country that will not like to do invest in Bitcoin.
I will not be surprised if I see many countries like Russia coming out to invest in Bitcoin because many countries don't believe in Bitcoin and currently they are the countries that want to use the opportunity of Bitcoin to improve the standard of their country, the people having issues with Bitcoin are the government and with the way things are going the government have started to know the value of Bitcoin.