Kotlin

Kotlin has experienced an accelerated rate of adoption and rapid growth of tooling support. Some of the reasons behind its popularity are its concise syntax, null safety, ease of transition from Java and interoperability with other JVM-based languages in general, and that it doubles as a great introductory language to functional programming.

It's the official Android development language and we used it successful in some projects and think it should be considered each time a java based application has to be developed.