I use Scala. Huge fan. Both for work and personal projects. Not wildly popular, so i get asked this by my team. This is what i tell them:

Focus on the patterns, design and theory. Those last longer than the language. What is enabled by language? What is difficult? What does the type system let you prove? How do you utilize the type system? How does the execution of the language work? What is the runtime like?

Language development itself has evolved. There is no longer a huge jump from one language to another because, well, we've figured out a lot of it. Want to learn rust? The patterns and concepts you learn with Scala will still apply. Go? Same, just a different form and you'll probably be asking about monads in short order. :)

If i look at future trends. Real far stuff. Stuff that will only become popukar years from now. Well, some of it exists now in esoteric languages. Those languages wont be useful for jobs, but studying them now preps you for the future.

Elixir is further future than Go. Go, like Java was, is not particularly novel but a very solid implementation of what we currently know.