I notice there's no Lisp on your experience list. I think you better do CL or Scheme (or Emacs even?) instead. :P
Learning lots of different languages is great. Lisp, Haskell, and Assembly especially changed the way I think about code in any language.
I like Rust, but if you did Haskell, the type system is going to feel like a limited version of that. The borrow checker is a cool, unique thing to try out though.
Nim is interesting, but I don't think it has any unique features that would encourage me to try out. Zig is another one that might be worth considering. It felt a bit like C with Lispy metaprogramming, but it's been a while since I did anything with it.