Programming is a way of thinking, not writing code in programming language X: that is "coding", not "programming".
By knowing at least something about more than just one programming language - preferably across different paradigms, so imperative/OOP/functional/logical - you train that way of thinking about problems outside the context of the specific details and quirks of language X.
I think this always improves your abilities to be(come) a better programmer tremendously.
