I know that you asked for a new programming language to learn.

But if you want to increase your skills as a programmer I think that learning algorithms and data structures that you don't know is better for your development than learning new programming language ( this book is a good one: http://en.wikipedia.org/wiki/Introduction_to_Algorithms ) .

While learning hard algorithms and data structures you will also learn how to think in a new ways. Also I recommend reading about concurrency and parallel programming ( general texts, nothing language specific ).

This will help you in writing better code in any language and also in understanding code written by others.