I think once you know 2 (or 3 if the 2 are as similar as, say, Java and C#), picking up new ones is comparatively easy. New paradigms can be challenging (looking at you, Prolog and Haskell) but quite doable.

However, if you resent being forced to learn a new language, or if you are more of a copy/paste developer than someone who really understands what you're doing[0], yeah, a new language can be a very challenging barrier.

[0] I want to be clear: most people start out with very little clue what they're doing in programming. That isn't meant as a disparaging description. I wrote (and copy/pasted) a hell of a lot of code before I started understanding the underlying mechanics of it all, and I'm still baffled by a lot of the development world (again, hi Prolog and Haskell).