Ever since the Google I/O keynote, developers have been wondering whether they should stick to Java or start focusing on Kotlin, which is now an official programming language for the development of Android applications.
The truth is that as opposed to Java, the resources for learning Kotlin are scarce.
Java vs. Kotlin shouldn’t even be a question to you considering you are already an advanced developer. Seriously, you are in a stage where both Java and Kotlin are BOTH at your disposal.
Similarly to Swift, you can bet on it that Kotlin will become increasingly important over time as well.