Kotlin announcement 2017/5/17: https://android-developers.googleblog.com/2017/05/android-an...
Swift open source 2015/12/3: https://developer.apple.com/swift/blog/?id=34
Swift open source 2015/12/3: https://developer.apple.com/swift/blog/?id=34
Kotlin was open sourced around 2012 and people were using it in Android apps before Google officially started supporting it in 2016.