Wow, it took 15 posts for someone to come up with german.
For the people who tried to unite the world twice we are really underappreciated.
I'm also sure that Germany is the place where you can find people who speak neither proper english nor spanish, the bakery across the street sells "Donat"s after all...haven't checked their spanish though.

Well, and then there is ancient greek, I think my latin teacher knew that.

The Dutch mostly speak german as well by the way, as do the Spanish, at least the ones on Mallorca.

Concerning mandarin, don't most Chinese, especially those in business, know english?

Spanish and italian both have some latin roots, of the two I would choose spanish, mainly because it's spoken in a lot more countries.

But in the end I think there are more ways than learning a language to prove that you're not an ignorant American, for example I could send you my own self-made inofficial "not an ignorant American"-paper badge for just 500EUR plus package and shipping.

Or you could just travel the world as you plan to, or just inform yourself about the world outside America.

And last but not least, I hear there are people who have nightmares from trying to learn french.