Jython has a new maintainer so it’s comming back as an option (I’d treat it as experimental for now). There’s also HABApp for a pure Python environment. Groovy is still around of course and there’s a Java automation add-on on the marketplace.
You’ve got options beyond JS and Ruby.
Though, for the most part 80% of your rules are going to be interacting with OH and for the most part OH’s API is presented very similarly no matter what language you are using. JS in particular is pretty similar to Rules DSL in how it’s interactions with OH are structured. It’s almost a one-to-one translation to port from Rules DSL to JS if you don’t take advantage of some of the nice additions JS adds which Rules DSL simply does not have (e.g. time.toZDT(), rule builder, etc.).
The actual quirks of the language tend to fade into the background. This is especially true for managed rules where the only place where you actually have to deal with the language is the Scripts part with the whole rest of the rule (triggers, metadata like name and tags, etc) being handled independently from what ever language you choose.