Hello, Witcher 3 key has regional restrictions? I can activate CIS key on România?

I don't think there are any region restrictions. The only effect your region has is the price of the game.

I did hear somewhere where you couldn't buy game codes in lower priced regions however. This probably is to keep people from selling game codes from low cost zones to gamers in high cost zones. Although this is pretty dumb as anybody can buy the game from GOG at any regional price they want (with the use of VPN).