From the Scala IDE
page on Android development: http://scala-ide.org/docs/tutorials/androiddevelopment/index.html
The Scala library therefore needs to be embedded in every Android application that uses it.
That seems a huge disadvantage to me. Both in terms of app download size and storage/memory size of your application. Unless there was a compelling reason otherwise (like you know how to program Scala, not Java, and don't have time to learn) I would say do it in Java.