Very interesting article! I like the fact that you mentioned Prolog as one of the less mainstream languages to learn. During my time at uni I found that both Haskell and Prolog really changed the way I approached different problems and gave me a high level perspective to problem solving. Some interesting resources to learn Prolog:
# http://people.cs.kuleuven.be/~bart.demoen/PrologProgrammingC...
# http://www.cs.bham.ac.uk/~pjh/prolog_module/sem242.html
# http://www.learnprolognow.org/
I'm getting an itch now, I think I'll give Prolog a second go this new year.