I've been thinking about learning another language sometime in the future. I know there are benefits to learning languages simultaneously, but I'd rather wait a few years before introducing another one. I like to do as much immersion as possible, so I think I'd be overwhelmed if I was trying the immersion method for another language. Plus, I don't know what language to choose.
I believe that "creating a need" is an important part of language learning. I have to ask myself, what other language would we have a need to speak? Of course I could pick Italian or French for the fun of it, but I don't know if I'd stay motivated because I can't think of a situation where I'd need to use those languages, and I don't know if I'd have easy access to native speakers.
Mandarin is popular these days, but I don't know. I can see potential problems with that.
There are so many different languages in the world, it seems a shame to limit yourself to one or two. I am going to keep thinking about it, but for now I guess I have enough on my plate with trying to increase my Spanish proficiency.