With many common languages, "learning" the language has more to do with learning APIs and minor syntactic quirks. You'll learn more if you chase after languages

With many common languages, "learning" the language has more to do with learning APIs and minor syntactic quirks. You'll learn more if you chase after languages with very different models of computation. Languages I've found particularly mind-blowing: Perl (esp. coming from C++), Scheme, OCaml, Prolog, Erlang, J / APL.