The more languages you get a chance to learn, the better off you will be. It has been a recognized fact among project managers that programmers who know more languages are more effective regardless of the language for a particular project.

Perl, C, C++, Java, JavaScript, awk, C# and several other languages are all quite similar to C. Perl, C++, Java, and JavaScript each have their own features and niches, but someone familiar with one can easily read code written in the others. Naturally if you know any of the C-like languages it makes learning one of the others that much easier. (The same principal applies to real life languages. French speakers have an easier time learning Italian than the Japanese do.) So instead of worrying about which brackets to use or how a for() loop works you get to focus on the strangeness unique to each language.

This process of learning the strangeness of each language will benefit your coding in any language you work in. Having seen the Perl solution to something can help influence the easy way to do something in C++. Having seen a massive OOP hierarchy in Java may make you want to create something similar in Perl. It all feeds back on itself if you're really learning.

After you've gotten a few of the C-like languages under your belt, consider learning some of the strange languages. Forth and PostScript are like nothing you're used to seeing. They will change how you think. LISP and Prolog deserve more than a passing glance. Everybody should write at least one non-trivial assembler program, but write a trivial one if that's all you've got time for. There are hundreds of specialized languages, from SQL to Mathematica, which are interesting each in there own way.

There's no reason to run out of languages to learn. Just like books, they're being invented faster than anyone could hope to consume them.