How? I just have a hard time imagining how a place with dozens of languages and cultures (I think that cultures with very different languages are likely to be very different from each other) and all of that can be less varied than a place like the US.
They still speak English, though, just like the vast majority of Americans. Europe has a huge number of different languages, and especially in Southern Europe it's not uncommon for even young people to not speak any English at all - meaning there's not even a common language that all Europeans speak.
I'm certainly not saying that all of US is the same. I'm saying that the differences are smaller than the differences you see in Europe. And I'm saying that as someone who've lived in the US and Europe and visited a great number of European countries.