It's also the only viable language with a decently sized community that allows you to write mostly FP or even fully FP code on the JVM. And one strength is that

It's also the only viable language with a decently sized community that allows you to write mostly FP or even fully FP code on the JVM. And one strength is that you can go from OOP via OOP+FP to fully FP if you want. Yes, that can also cause a mess, but for learning it is one of the best languages out there imho.