On the KillerPHP.com site there's a new post that compares two popular languages - PHP and Python and tries to answer the question "Which one should I learn?"
One question I get often, is which programming language should you learn? I’ve been getting this question for years!
Things change in the programming world, languages come and go. But the good news is that the basics, the core concepts and techniques, are 90-95% the same in all the modern programming languages. [...] What that means, is that your programming language choice, isn’t nearly as critical as you’d think. Why? Well, once you know one programming language, it is easy as apple pie to switch to another!
He then gives some of his own thoughts about how you could decide which language you should pick including the kinds of programming (target result) and what kinds of jobs you can get with each.