This interview with Lua’s designer is refreshingly to-the-point. The last paragraph is worth repeating in full here:

More seriously, I really subscribe to the idea that "if the only tool you have is a hammer, you treat everything like a nail". So, programmers should learn several languages and learn how to use the strengths of each one effectively. It is no use to learn several languages if you do not respect their differences.

That last sentence says it all. It implies learning several languages well - not just skimming them to pick on some perceived flaw. All major programming languages are trade-offs, and more often than not incredibly well thought-out. To put it differently: if you can’t find an aspect of language X at which it is substantially better than what you’re using most of the time, then you haven’t understood X.