I can teach any developer Rust or Clojure in a couple weeks. I've only done a few hours of Rust study myself, and just minutes in Clojure and yet I will say that with confidence. It takes years to master, but the difference between 1 month and 10 years for an otherwise experienced programmer is not very large - either way the hard part is the problem domain, understanding your code, and other such details not related to the language. HR puts far too high a weight on skills in a programming language, in part because they are easy to measure while the ability to write good code is hard to measure.