There’s a kind of qualitative difference between a game that was built to be played and later has DLC released for it and a game that is essentially built as a DLC platform. The latter has become extremely common in AAA games and it winds up feeling incomplete because the insertion points for planned DLC are usually quite noticable.
The above is pretty misleading. A typical Java program can be made into a Kotlin program with little changes, this is true. But Kotlin code, particularly when written using Kotlin best practices, bares very little resemblance to Java code. If you learn Kotlin first, you’ll find some of that knowledge does transfer to Java but then there’s plenty that won’t and you’ll have to learn the Java way of doing things too. Still, as a dev, knowing more languages never hurts. I’d still recommend proceeding with Kotlin.