It depends on what you want.

I learned Haskell some years ago and even though I never used it for professional development, it paid off in the sense that it allowed me to reason about my code in a completely different way. I became a better programmer because of that, no matter the language in use.

There are a bunch of cool languages to choose from: Elixir, Haskell, OCaml, Rust, Crystal, Pony, Kotlin, etc. Pick the poison you get more interested in and go for it.

Hi, what languages do you already know, what kind of software are you mainly looking to build or are you mainly learning for the sake of learning?

Personally, I’m currently really enjoying Go after two failed attempts at liking it over the last couple of years. This time around I’m finding it extremely liberating and fun!

The fact that it doesn’t come with a lot of bells and whistles makes me focus on what I am building, rather than trying to come up with clever solutions for how to do it.

In combination with a type system to support safer refactoring, fast compilation and the performance of a natively compiled language makes it feel like taking the positives from developing in a script language but without any of the negatives.

When choosing programming languages for you, you should be aware of versatility, personal interest, and industry demands. Here are some popular options such as Python, Rust, Kotlin, Swift, and R Language.
Thanks