- Functionally programming language
- WASM is good for beginners
Given that you’re already familiar with the Java ecosystem, you may want to check out Scala for a functional language. Kotlin also has a lot of functional aspects to it.
Given your background with C and C++, you may like the functional parts of the Rust programming language.
If you mostly want to gain new perspective from your newly learnt functional programming language, I recommend it be Haskell: it is sufficiently different from the languages you already know to force you to learn to think in different ways.
If you care more about practical utility than new perspectives, Haskell is unlikely to be a good fit. However, in that case I also have trouble seeing the point in learning a new language specifically because it is a ‘functional’ one.