I most regularly use Python, followed by MATLAB C++. Python has been practically mandatory for writing code for my undergrad research. My classmates usually know "a little" Python, and it's pretty easy to pick up on the fly. I'm trying to phase out MATLAB for Python seeing as I'll be graduating soon and my student license will run out. I know about Octave, but work done in Python is probably easier to integrate.
My favorite is C++. It's the first language I learned and it feels like home. It gives me enough abstractions to get actual work done, but it also has the low-level tools I need ~~to shoot myself in the foot~~ for working with Arduino or other microcontrollers.
I'm looking into Rust for audio programming. Although audio programming is done almost exclusively in C++ these days, Rust's safety features without performance penalties look like a promising language to write fast and reliable code suitable for real-time operation. Joining Lemmy and seeing how it compared to Kbin has cemented my interest in the language because so far, despite the bugs I've run into, Lemmy and Jerboa has been fast above all.