neniro said this earlier, and I completely agree with him. Perl is an incredibly powerful language that can do nearly anything. However, learning other languages helps any programmer think in different ways, which ultimately leads to finding the best solution for a problem more often. Some people rave about functional programming. Other people rave about Object Oriented Programming. Other people rave about AI programming. Other people rave about this and about that. It's true that a programmer can get Perl to do all of those things, if said programmer understands all of those things well. Learning other languages gives any programmer those tools because he or she understands the concepts and the best way to do things in that style from learning a relevant language. Learning other languages brings that all back to Perl to make the programmer more effective. If the programmer were just expanding his or her knowledge of Perl, sure, they'd end up picking some of that up just from Perl, but the programmer wouldn't have the deeper understanding of it, so would feel less comfortable using it to solve a problem.

    -Bryan