Earlier quoted context omitted.
Dart doesn't have the adoption yet and has a different plan when it comes to mobile ( https://github.com/flutter/flutter ). I love Go, but it's not really a suitable language to do UI, or anything that deals with data models. C#, however, is a perfect replacement for Java, most of the times. I would say "it's simply superior in every imaginable metric other than cross-platform implementations of the compiler/VM" but…
Nothing can replace Java for android, unless it can also replace all the libraries current Android application is replying, which is the reason why I believe Google isn't going to switch off Java anytime soon.
I doubt it will be officially acknowledged by Google, but hey they never acknowledge third party good things, and the official Android developers docs still tech us to do networking with HttpUrlConnection and threading with asynctask, we moved on to okhttp and retrofit and rxjava anyway