You have some great answers already. I think there is no single answer to your question. What language(s) you choose to learn depends on what you intend to do.
When I was a graduate student I too learned some Matlab, Mathematica, Maple, SAS, Stata, because my university had licenses and because in my area of research that’s what others used, so I could easily take existing programs and modify them to my needs. That was a while back. I have since dabbled in Python, Julia, and some statistics software like R and Stata. So what would I recommend?
It’s a multidimensional decision to make. Here are some criteria based on my limited knowledge (I haven’t tried Ruby, another popular choice):
- Open source: Forget Matlab and Mathematica. Go for R, Python, Julia, C++ and all that. I avoid proprietary software whenever possible.
- User base: This depends on what you do. Go