As Lee said, it will really depend on what you are planning on doing with your career. If you really want to be a successful developer, you need to be familiar with more than just one language. That will not only help you get better jobs, but many of these programming languages need to interface with one another. For example, if you want to work for an e-commerce development company, chances are you will need PHP, MySQL, JavaScript, Jquery and HTML/CSS at a minimum. Learning just one of those will not really give you much traction. You'll probably find that you enjoy working with one of those more than the others, but you really need at least a basic understanding of all of them.