Python, because of its power and maturity in programming.

Okay, okay… serious answer: ancient Greek, Aramaic/Arabic/Hebrew, and Latin so I could read primary texts of Judaism, Christianity, and Islam without a filter, thereby increasing the depth of my understanding of significant influences on the society in which I live.

If I could learn the Language of Life... Bilingual English Spanish already. Living in Europe met a lot of Scandinavians ladies but they all knew English and some Spanish... would had been nice to surprise them... Okay I will settle for German because I lived there too and got Great memories and interaction with the Frauleins.

I'd actually learn French and Russian.. hehe..Dunno why but it's a weird mix haha

French and Turkish

Good question! I have several I'd like to learn or improve my abilities in. 1) German--I have a master's degree in it, but if you don't use it, you lose it--so maybe a few weeks at the Goethe Institute in Munich? 2) Spanish--when the Trumpets start putting on uniforms, it's time to go, and I'm thinking Ecuador or Uruguay or Chile. 3) Korean, which I already have a basic knowledge of from the time I lived there, but would like to improve for my occasional visits.

French, Swedish, Italian and Russian.

I've got a degree in Russian and German and speak French so I would go Chinese next .

I’d learn a lot more ASL than I can feebly “speak” currently.

I speak Spanish because i'm from Chile, and i also have a pretty decent level of english, but I'm currently trying to learn Dutch, because i'm moving there in a few years.
So if anyone needs some spanish practice, im totally willing to help.

spanish as there are so many countries that speak it , old and new world

I would learn italian because I am italian and can not speak one word of it .When I visited Sicily last year I would have loved to be able to speak the language .

Italian. It sounds musical and beautiful. Next time I go to Italy, I hope I can understand a little bit what the label says next to a marvelous artwork in the museum. No google translate can't do the job though I do use it often

I'm currently learning Spanish. I think the language sounds really pretty. I've heard learning Spanish or French helps when trying to learn other Romance languages.

Since it is the only other language I hear regularly other than English, I'd go with Spanish.

Funny you should ask. I had an aunt that I was very close to. She lived and worked in Germany and I got interested in that country. Joined the German club in HS and was trying to get stationed there while in the military with no luck. Nothing but pure luck presented an opportunity to go there after my military was over, and I took it. I not only got to learn the language but live in the country for 15 amazing years.
Incidentally, I learned that knowing another language goes a long way in having an insight in other cultures.