What language(s) do you recommend for a bilingual speaker to learn?

I speak English and Spanish. Spanish is my first language, English I learned once I moved from Puerto Rico here to Philadelphia.
I am interested in learning more languages (maybe 2 or 3 more) because I would love to know more than 2 languages. I have a feeling knowing more than 2 languages can open opportunities in life and I am willing to put my effort into it. From what I am thinking, I want to be either a mechanic or a firefighter. It seems as though I will not need to know more than 2 languages for these jobs, but hey you never know. You say you want to do this, or be that, and end up doing something completely different (not necessarily true ALL the time). I just want to be prepared is all.

* I began learning Arabic but got expelled from school so I couldn’t learn is as well as I wanted to (I understand this is not an excuse to continue learning the language, but after that I slowly began to forget the language since it was something I was not practicing each day)