Two points for using Swift on Android: 1) shared code between your ios, mac, and android apps. 2) you already know swift.<p>That said, there is always a cost to using a non-standard language to develop for a platform. Things like having to translate documentation as you read it, friction between system libraries and your languages standard library, etc.<p>I&#x27;ve not looked at Kotlin in detail, but I wonder how much that friction is reduced because it&#x27;s java-based, or if you&#x27;ll experience just as much friction using Swift on Android as you would using Kotlin on Android. Worth evaluating if you&#x27;re starting a project 6 months to a year from now as the Swift tooling for Android starts to mature.<p>As it stands now, I would have a look at Kotlin, but almost definitely write any projects started today in Java. Swift is nowhere near ready, and the advantage of writing in the platform&#x27;s &quot;native&quot; language usually outweighs any benefits there are to using a &quot;better&quot; language.