Yo got time to lean, you got time to clean (Score 3, Insightful)

As always with these sorts of questions, the answer is "it depends". If you are employed and working with Java or C++ or something else, then by all means be the expert in these languages. Once you get to the expert stage - might take a year or two or three - by all means expand and be a generalist in many languages, but continue being an expert in your favorite language. I can tell you that those COBOL/RPG programmers in this great land are within ten to fifteen years from retirement, and there is a-whole-lotta code out there that still needs love. Since Y2K, I don't know anyone under the age of 40ish who is writing COBOL/RPG, so there is an opportunity there, if you are so inclined. If you are unemployed, then do one or two projects in your favorite language and one or two projects in a language that is used on your prospect list. For example, you want to work for Twitter? Learn Scala. Regardless, as the old adage goes, if you got time to lean, you got time to clean, or in this case, code. Good luck, and good question.