I‘d say it depends on your motivation and your reasons for learning another language. Do you want to build something in particular? In that case, pick the right tool for the job, as the others have suggested. However, if you want to broaden your horizon, I would suggest to try a language based on another paradigm, e.g. a functional language such as Haskell, ML, or OCaml. Want to see some „pure“ object-oriented language? Then maybe have a look at Smalltalk. The languages I have listed may not be the most widely used in practice, but in my experience, knowing several different programming paradigms makes you a better developer overall.