This depends a lot on your situation. If you work for a medium-to-large company, you may be called on to learn new technologies for new projects, new business

This depends a lot on your situation. If you work for a medium-to-large company, you may be called on to learn new technologies for new projects, new business initiatives, etc. If this happens too often it can be a bad sign, but in moderation it's a great way to learn new skills, broaden your horizons, and deepen your toolbox, so you can always find the right tool for the job (which often changes over time, since as an industry we are always enhancing our toolset). If you are a freelancer or in a small startup, this is much more at your discretion. You'll still want to use proper tools for the job, but you can make use of what you already know, or try out the latest whizbang thing. The common thread is that for the most part, the technology used is secondary to the business needs and how to fill them. By all means explore new languages for your education and edification, but if you are asking "Do I need another language," the answer is, "Can I use it as a tool to solve a problem I am facing?"