Somewhere some guy said (I honestly do not know where I got this from), that one should learn one programming language per year. I can see where that might be a good idea, because you learn new patterns and ways to look at the same problems by solving them in different languages. Typically, when learning a new language, I look at how certain problems are supposed to be solved in that language. My question now is, what, in you experience, are good, simple, and clearly defined tasks that demostrate the differences between programming languages.
The Idea here is to have a set of tasks, that, when I solve all of them in the language I am learning, gives me a good overview of how things are supposed to be done in that language. I do not know if that is even possible, but it sure would be a useful thing to have.
A typical example one often sees especially in tutorials for functional languages is the implementation of quicksort.
Search for "Code Kata" for some resources.
Pick a problem. Solve it in different languages.
http://slott-softwarearchitect.blogspot.com/2009/08/code-kata-resources.html