C# look like a dead end, though much better than first WinPhone with "SilverLight." If you have written c/ or c++ engine, you need just a good bridge to OS UI language. Well, also platform + tools that work well on each Unix/Linux.

Just to mention I used to like MS technologies. Least problems I had with ASP 2 / AJAX web app which works for nine years without significant problems.

>"C# look like a dead end"

http://statisticstimes.com/tech/top-computer-languages.php

> "you need just a good bridge to OS UI language"

For moblie apps, Xamarin is that bridge (can always build web apps too):

https://www.xamarin.com/

Plus, .NET Core is cross-platform, good cross-platform tooling becoming available (VS Code, etc...), and you don't have to use C#.

If you're interested in writing games, Unity uses .NET (Mono in particular):

https://en.wikipedia.org/wiki/Unity_(game_engine)