Elixir, Haskell et al. require concepts that are not required at all in e.g. Java. The functional programming module at my university had the highest failure rate after the math and statistics classes. Even something like C can require new concepts. I was a tutor for a university C programming course and students that had no problems with Java struggled hard with direct memory manipulation, pointer arithmetic etc., b…
If you only know java are you even a real (professional) dev? I'd expect any dev wanting a job using a language he doesn't know to have some understanding all of the concepts you're talking about. It's not language specific, it's just the basics of programming.
Hum... Do you write programs in exchange for money?