(1)
Anticipate that at some near-future time you will have the opportunity to work on yet-another language that you haven’t used before. Therefore, make it your business (since it is “your business” ...) to familiarize yourself with as many languages as possible. (I happen to think that it’s fun.)
(2)
Also assume that new languages will always be coming on to the scene (e.g. Apple’s now open-source [Tom?] Swift), and that languages now in use will never die. On the one hand, people are always looking for new and more-efficient ways to build certain things (and so, they are designing languages for that purpose), and on the other hand, they accumulate a vast monetary investment in the systems that they already have. Be their solution to their problem, no matter what it is.
The more nimble you are ... and the more you’re willing to say “sure, I can do that,” and never let them see you sweat, and somehow make-good on your promise ... the more marketable you will be. It does not matter that you focus on “one or two languages” for extended periods throughout your career. (Everyone does that.) You will find that it all comes right back to you. If the next one’s in Perl (5, or, who knows, 6?), jump in. The water’s fine.