It's always a good idea to be competent in more than one language. For two reasons:
1) it gives you more opportunities and options and prevents you from being pigeonholed
2) the more languages you learn the faster you'll pick up the next one - giving you even more flexibility
As some other people have commented, you should choose your next language based on both what sorts of project you'll be able to build from it and what you'll learn from it (be that working with pointers, a completely different syntax family, or a programming paradigm that's new to you).
1) it gives you more opportunities and options and prevents you from being pigeonholed 2) the more languages you learn the faster you'll pick up the next one - giving you even more flexibility
As some other people have commented, you should choose your next language based on both what sorts of project you'll be able to build from it and what you'll learn from it (be that working with pointers, a completely different syntax family, or a programming paradigm that's new to you).