It will create a temporary rise to the price of Bitcoin. That's the impact.
Since most of the altcoins follow Bitcoin's price movement, there's a chance that they might increase as well, but not as much as Bitcoin.

After that, it will be back to normal. Do you expect that Bitcoin becoming a legal tender to these 2 countries have a long-term effect towards the price? I don't think so, and TBH, I don't see this ever happens as well. I mean China has banned Bitcoin at first place, and until now, there's no sign that they're unbanning it. Well, if for some reasons this will happen, I don't also think that there will be an increase in daily transactions as well because I believe people would rather hold their Bitcoins rather than using it to pay something especially now.

I guess let's just not expect for this to happen.