The readability process at Google is a way to gain the ability to submit code without a language style reviewer. To submit code into google3 (their main repo for server-side stuff), a changelist requires acceptance by a person or people who collectively own all of the code being changed, and a person or people who collectively "have readability" in all of the languages in the change. The simplest example is there is some C++ code that you own and you have C++ readability. In this case you need the review of anyone. If you don't have C++ readability, you need a reviewer who does have it, and they need to carefully review your change for style.

It used to be that you had to do a "readability review" which was a large change that you developed specifically to gain readability in some language. A style reviewer would approve it after (usually) many rounds of comments, and then thereafter you had C++ readability forever.

More recently some language teams have adopted incremental readability. In this process you add a language reviewer to all of your changes, and after you demonstrate that you know what you are doing, they will grant you readability. I think the Go team was the first group to adopt incremental readability, but it spread to other languages.

This process is off-putting to people who want to join Google but not be acculturated to their language style rules. There's a surprising number of these people. In mainline Google these people simply will not get bonuses, raises, and promotions. In defective organizations like Android they just discard Google code quality standards and it shows.