In my opinion, early on in your career the important thing isn't so much what language you are developing in, but who you are developing with. If you aren't in an environment where there are more experienced developers that you can learn from, find a different job. Over time you will probably move through several languages, but the core principles of programming apply to all of them, and learning how to think through problems from a developer's perspective is fundamentally important.

Another bit of advice would be to work in a position where you have your hand in all aspects of a project. That will help you decide if you want to focus on a particular subset of application development (i.e. back-end, front-end, UX), or if you want to move forward as more of a generalist. This decision will impact your future type of employment. Concentrating on one particular aspect of development will lead you towards larger companies and/or larger development teams. Being a generalist will lead you towards smaller companies or start-ups with smaller or no teams at all, as well as possibilities outside of normal technology companies (i.e. I am interviewing with a law-firm next week that needs a senior developer to create internal tools). I'm of course speaking only from my experience and making generalizations on that basis alone.