At the moment, Rust isn't an "officially supported" language, but a "community supported" language.
Someone is working on it here: https://github.com/GodotNativeTools/godot-rust
You can get it now if you want. It looks like you will need to compile it.
I don't know if it can be considered "finished", but getting involved and sending feedback is a good way for it to progress.
It only works in Godot 3, because it has to use GDNative, which is not available in Godot 2.