It would be strange to create such an OS, which is why that's not the case of Fuchsia:

"Fuchsia is designed to let developers bring their own runtime, which means a developer can use a variety of languages or runtimes without needing to change Fuchsia itself"

Sounds very much like any Apple, Google, Microsoft, IBM, Oracle, Sony, Nintendo, pick your embedded OEM, ... to me.

UNIX has always been the snowflake, and even there, commercial UNIX SKDs are pretty much C, C++ and Fortran, followed by the usual POSIX scripting languages.

To create a good developer experience in OS SDK IDE and platform APIs, there are only so much one can support.

Unless we are doing UNIX ABIs and the best one can hope for are 70's C style bindings.

To the extent that there's native C++ I'm sure it will be somewhat straightforward to get other languages supported later by users/developers.

2-3 languages? It has support for C, C++, Dart, Rust, and Go. And I think some level of support for Swift.

I wouldn't be so sure about Go. Anway, I found certain remarks somewhat irritating in this respect. I'm happy if it turns out I misunderstood something.

Go is listed as a language https://fuchsia.dev/fuchsia-src/development#languages

I see they pulled their language policy from a few months ago. Good.