My Oldest is already starting to take Spanish. She was debating Mandarin and I told her Spanish would probably be used more then Mandarin.
If someone talks Spanish and I'm around it for a few days again I'd start to at least understand it again to a point. Used to be around it a lot more and I could understand the conversation enough, but like anything else once you don't use it the skill is lost....at least until you practice again.
Good call there, Spanish is way more universal. While Chinese people are all over the world they generally speak another language anyway. Not to mention you have to be a natural liguiest to even attempt to learn it.