Times have changed. Languages are essentially irrelevant; if you have a reasonable background, you can pick up whatever languages (note plural) you need.
The question a couple of years ago was "what libraries?" There's probably a library that does what you want; use whatever language it's written in. Yeah, I know, everything eventually reduces to C, but like most things, it ain't that simple.
The question now is "what frameworks?" Nowadays, you don't develop programs from scratch; you start with a framework and build on it. Using Ruby on Rails? Write in Ruby. Using Django? Write in Python. Node? Write in JavaScript. Hadoop? Write in Java.
That said, the only two languages that it's really necessary to be fluent in are C and JavaScript. C is, of course, the language that most of the rock-bottom stuff is written in. A lot of systems produce C as intermediate code, and, as a result, a lot of C-isms tend to sneak into places you wouldn't expect. Learn your pointers. JavaScript is the only language that will run inside a Web browser *; if your code touches a browser, it will use JavaScript.
* Yeah, I know; Java applets. I don't know which is more painful -- writing them or using them.