if Russia agrees to have BTC as legal tender, where would the Ruble be? It would be a double-edged sword for Putin, because everyone would buy pure crypto, and the currency would simply lose more and more liquidity, because you can't compare a government-backed currency to BTC and everything that has to do with crypto. In addition to the fact that the inflationary economy will always be below the economy that manages BTC, any deflationary economy will have more influence and much more guarantee than the traditional economy, it is no secret to anyone that the high hands in Russia manage BTC.
The idea is that if they do this, then they could make sure that they sell that bitcoin for ruble and gather all the ruble all around the world. Not just inside their nation, but get bitcoin from others, and this would earn them a ton of bitcoin, then sell it and get dollars, or euros, and then they could sell those and get ruble.
What this does is put a lot more dollars into the world since they are selling it, and taking more ruble out of the circulation because they are buying it. As we can see, that would work. However, they are already doing fine to be fair and I do not think that they would need something like that at this point.