Did you think about Kotlin? Has the benefit of being backend, frontend, and mobile-friendly plus it's a functional language.

I've been working on a project that is part Java and part Scala - the latter is so much easier to work with and it forms the backbone of many big data frameworks. It is definitely niche compared to Java but that makes it more desirable if you have skillz.

But whatever language do yourself a favor and get a copy of IntelliJ, it's a great tool and the free version for Java/Scala (maybe Kotlin too, I haven't checked) has all you need.