Hi Piet,
I'll do my best to answer your question, but please keep in mind that my knowledge of Kotlin is quite limited ;)
While Kotlin could be considered a better
Java, Scala is a language that, although highly influenced by Java, wants to do things differently from it -- one of the reasons why learning Scala for Java developers can be at times a bit overwhelming.
Scala's main goal is not to fix Java but to combine two programming styles that are very different: OOP vs FP.
Have a look at this article on the subject, which I think is really nice:
https://dzone.com/articles/kotlin-vs-scala-vs-java
Cheers,
Daniela