Thorsten Ball writes on his personal blog:

Different programming languages are good at different things and bad at others. Each one makes certain things easier and in turn others harder. Depending on what we want to do we can save ourselves a lot of work by choosing the language that makes solving the type of problem we’re facing the easiest.

That’s one of the tangible, no-nonsense benefits of learning more languages. You put another tool in your toolbox and when the time comes you’re able to choose the best one. But I would go even one step further.

I think it’s valuable to learn new programming languages even if — here it comes — you never take them out of the box.

But why?

Languages shape the way we think, each in their own peculiar way. That’s true for programming languages as well…