I only have this issue with one language: C -- which I rarely use, don't much like using, don't much like, but still want to remain somewhat familiar with. I've remained familiar with it by habiting Freenode ##C , which conveniently has some regulars who I like talking to about non-C subjects in between C questions. On a C question, I answer or otherwise help the questioner (... ask a better question) until someone more knowledgeable notices.
For Perl, Freenode #Perl seems like it would offer similar opportunities. You can also answer questions here, of course :-)