For fun: Crystal seems totally awesome (though it'd be nice if it would start faster), mruby should be a small and useful jump, there's apparently some streaming language that Matz is looking at, I'd be willing to play with it. SpaceX is using some visual programming language, that sounds like a fun paradigm. Python would let me play with Tensor Flow. Idk, maybe Idris or Prolog just to get an extreme exposure to their respective paradigms. OCaml could be fun for a certain subset of playing around (namely parsing). Common Lisp, Chicken Scheme, and Racket all have interesting aspects that make them seem like potential choices within the Lisp world, and I find that world to be fun.