[OskarS]

I agree, especially if the other language uses markedly different paradigms. Like, if you already know Java, learning C# is not going to massively expand your horizons, the languages are too similar.

Instead, you should try something like a functional language (like Haskell or a Lisp variant), or a dynamically typed language (like Python), or a language with a different memory management model (like C, C++ or Rust). It will give you practical skills and expand your horizons on how to solve problems with programming.