Ask HN: Languages Worth Relearning?

Programming languages evolve at different speeds. Sometimes there are huge breaking changes, sometimes backwards compatibility keeps things rather stale. And occasionally it's like Python 3.

So tell me about languages that have changed enough to be worth learning new, either because now the language is actually worth it, or because paradigms changed. How does the community deal with it, do we now have two or more different languages subsets in play (C++) or has almost everyone moved on (Javascript)? Do we have cases where the language (mostly) stayed the same, but the library/tool/community changed enough for it to be considered "new"?

Examples would be Javascript/ES6, C++17 or Java 8+, but if someone wants to go on about Fortran 77 vs Fortran2015, I'm more than okay with that.