I commend the exercise! In terms of sampling points in programming-space, I often recommend Prolog, though I think that might not be well suited to your goals here (you're not likely to run into a managerial situation where someone is pushing it...). Two things that probably belongs on either kind of list would be Haskell and some sort of Lisp.
I think Lisp is a great language and every programmer should at least glance at it. It can really change the way your brain works (in a good way).
I would probably also add Rust to the list. Its slowly replacing Go in my mind for system level things. :/
It's a little bit pedantic, but Ruby on Rails, Node.js, and Arduino are not programming languages. Also, C/C++ is not one language but two. But I don't suppose that detracts from the value of the exercise.