alt Hacker NewsInterestingly, Kotlin has a pretty solid cross-platform story.
I'd pick it over Swift if targeting Android since it can build and run in the JVM as well as natively -- and has Swift/ObjC interop. Its also very usable on the server if you wanted to, since you can use it in place of Java and tap into the very mature JVM ecosystem. If that's what you're into.
And I have a lot more faith in JetBrains being good stewards of the language rather than Apple, who have a weird collection of priorities.
Kotlin is practically a no-brainer when you have JVM at your finger tips, versus something like Swift which is comparatively young.
I tried to use Vapor with Swift recently and struggled to get something working because the documentation looked comprehensive, but had a lot of gaps. I ended up throwing it out because I didn't have the time to dig through the source to understand how to do something, when I could use a mature framework in any other language instead.
The promise is there but I'm just not ready to invest. My youthful days of unbounded curiosity are coming to an end and these days I just want to get something done without much faff.