As an amateur game engine developer, I'm probably in a weird minority for abhorring C/C++/C#/Canything. :)
I love Swift, and Rust or Dart would be my next choices if Swift wasn't available.
With first-class support for native APIs which do most of the work anyway, performance has not been a concern for me on Swift. I see only benefits, like making it hard for some types of bugs to creep in and code that is pleasant to read and a joy to write (though you can write beautiful/ugly code in any language, of course.)