If you change source files in language X, someone proficient in language X (aka "has X readability") should approve that it corresponds to Google Code Style in language X.

You start without it and may obtain once you've written a bunch of code in language X.

I'm not sure if there is really a Borgmon readability. But if there is, it seems like Borgmon configuration files are both common (so that there is a readability requirement) and uncommon (so that there are very few people with readability).

There isn't Borgmon readability anymore because of this video (the video is about 10 years old).

Borgmon is a monitoring system for Borg (https://sre.google/sre-book/practical-alerting/#the-rise-of-...), and it has its own language for configuring monitoring rules. The Borgmon language is infamously obtuse, and the idea of "clean" Borgmon code has basically always been a punchline. To be fair, the problem domain that it's in (declarative computation and reduction over high-dimensional datasets) is tricky to make clear, and if you use it exactly as intended, it can do some really cool stuff. But the upshot is that it has a high learning curve, a high propensity to degenerate into wallpaper, and a very small number of people who are sufficiently familiar with it to be readability reviewers.

It also doesn't help that "just copy-paste someone else's" actually does cover 90% of use cases, which both reinforced the idea that it was a chore and actually made it harder to gain readability, since being granted "readability" status requires writing a meaningful amount of non-trivial, non-copy-paste code.