If you include Javascript, it's very common. Beyond that, I've pretty well stuck with one language in production work for about five years. But that's only bec

If you include Javascript, it's very common. Beyond that, I've pretty well stuck with one language in production work for about five years. But that's only because I've mostly done modest-scale web app development, which really only requires one backend language. If you stick to web apps, you can go a long way with a single backend language. But my current startup is about 50% web app and 50% Linux app. So we're finding more and more need for C.