Concepts are what is important. Concepts are what separate skilled engineers from the common coder. Languages are tools which change often, but the fundamentals are generally constant.
I finished college with a healthy working knowledge of C and Java from academic and side projects. I had become extremely proficient in Perl and I also had a year of internship experience in C++. I interviewed for jobs focusing on all of those languages. My favorite was Perl, and I eventually accepted a position which dealt primarily a project that was Perl-based. Six months later I had to do a fairly complex Java project (lasted 3 months). Immediately after that I started a year long project in Objective-C, a language which I had absolutely no knowledge of. Now I hardly code Perl (I miss it, but I do not mind Obj-C much... I'm quite proficient in it by now).
The point is you never know where life will take you. I can attest from experience that switching to a completely foreign language stinks. It can be very rough initially, but if your fundamentals are strong, you'll have something to lean on instead of falling down. Not to mention that a generalist is an extremely valuable position to be seen in by your boss.
It's important to know languages, but they are secondary to mastering the fundamental concepts that you'll take with you for your entire career.