New programming languages could be introduced at any time. Knowing the right language might position you very well for a career opportunity in the future. Therefore, it might be advantageous for a developer to track languages like Java, C, Objective-C, Python, Ruby, and Perl to see which direction they are headed in popularity.
This infographic also gets into the history of some languages, vulnerability distribution per language, and how those vulnerabilities are being fixed.
Infographic (click image for full infographic):