Don't even need to learn Spanish. While the United States doesn't have an official spoken language, the official written language of this country is English.Seeing as English is the closest thing that we have to a worldwide language ( lingua franca, ) and American media itself is prevalent worldwide, this really isn't that much of a surprise.
I mean, what Language would we really need to learn in school? Spanish, since it's our unofficial secondary language? That's about it.