Besides, I would be highly critical of anyone who claims to know a variety of languages since it probably means they are only familiar with a strict subset of their standard libraries and quirks. Or that knowledge is incredibly outdated.
Learning the syntax is one thing, the more time-consuming for development part is always knowing the quirks and patterns used today.
Well with that argument, learning brainf*ck in depth should give you all the programming experience you need to solve problems efficiently :P
Learning even the basics of a functional programming language for example (Haskell in my case) lead me to understand why things are the way they are in a few other languages. Sure you can write some solution in a few nested for loops, but why not use a list comprehension if it's more clear and less error prone for the situation? Specializing in one or two languages isn't a bad thing, but I would argue that learning even just the basics of other languages is beneficial. Understanding what tools are out there and what they're best suited to is a good thing if you ask me.