Let me add just a bit to your comment on Spanish. Spanish is the single easiest commonly used, spoken language an American can learn. It has a TINY vocabulary (you can claim fluency knowling well less than 10,000 words). There are native speakers all around you who love talking to English speakers in Spanish (not only is it hilarious, the English speakers are buying things and helping them makes them repeat customers). It's actually USEFUL, and you can start putting it to good use right away in almost any state. Try that with German! And then there's what you said.
ASL is also dead-easy, but it's not spoken, per se, not really written, and only useful in deaf schools. That said, you lean ASL and you can pick up other SLs accross the globe faster than anyone can pick up a new spoken language, and there's deaf folk in every country.