Considering they have their own Manehattan, and so on, it is similar to America, yes. But it isn't America because it's a land of ponies, a whole country actually, right? So I'd say of course it is possible that they do have their own language called Equestrian! I mean why wouldn't that be a possibility? Maybe that would be a language close to english but still not, like their name of certain places. I'd like to believe it would be highly possible rather than just assuming it's english because it doesn't make much sense else that it is in english of course because it's a show with english speaking directors, animators and voice actors. But it is another place, a fantasy place, so for them to speak another language, yes, I find that highly possible!