I will say the FreeBSD handbook is such a breath of fresh air compared to other OS documentation. Everything is easy to find and well formatted. Same goes for the OS internals themselves. It's just a cohesive project altogether.
You're seeing the benefit of the cathedral model right there: a centralized, architected approach yields unified documentation, whereas the bazaar is inherently fragmented.
Back in college I spent some time translating portions of it to Russian. It was super easy to work with the project on that. I honestly have no idea if any of my contributions are still a part of it but I am really glad I did that.
same experience for me, I translated a few chapter to Italian while in university, I learned a lot and the translation project was super well run.