readability grants a code reviewer the power to approve changes in a specific language

It is a formal process via which it is confirmed that you know enough of X to submit code to the codebase, where X can be c++, java, python, etc. If you don't have X readability, then, in addition to your main code reviewer, you need to have a readability reviewer look at your code, who will be focusing only on X, not the logic of your code.