The more the better, but there's already a "European Yellowstone" in the form of Belovezhskaya Pushcha National Park in Belarus, of similar size, home to many of the remaining European buffalo.
There are also buffalo that are not bison, like the domestic water buffalo.
I know in Polish, "żubr", which is the European Bison, is often translated as buffalo and the American Bison is known as "bizon" which is understandably translated as bison. I would not be surprised if Belarusian was similar.
And buffalo (like African and water) is "буйвал".
I had no idea American English used "buffalo" and "bison" interchangeably.
Learn something every day. :)
But the bighorn sheep is really a sheep and it does have big horns, so they have that going for them.
My wife's Belarusian though, and I have been to Belovezhskaya Pushcha and seen these buffalo/bison beasties, so I've got that going for me!
The Dutch word for Alces alces (the animal called a moose in North America and an elk in Europe) is "eland".
Dutch settlers in South Africa decided to use that word for the large antelope of the genus Taurotragus, which is still called an eland in English.
Modern Dutch distinguishes the two by calling the antelope an "eland antelope", while Afrikaans calls the moose/elk an "American/European eland".