No discrimination of any kind. This includes any language likely to offend or alienate people based on (but not limited to): ...English fluency,...
It seems strange to say that we shouldn't/won't discriminate based on English fluency. I think the goal of including "English fluency" in the above list is to stop people from saying subtle put downs-downs like: "Did you pass second grade?", "Do you speak English?", etc. But that seems to be handled by other sections of the Code of Conduct. More importantly, most Stack Exchange sites must discriminate on the basis of English fluency.
For an extreme example, if a fluent Spanish speaker has zero English fluency, they should not and cannot post on the default Stack Overflow (English) site. This is true for most Stack Exchange sites. Of course the same would be true for non-English sites like Stack Overflow (Russian). The community members there discriminate against me. Since I'm not fluent in the language, I cannot post there.
The best possible interpretation of including "English fluency" in the list of attributes that cannot be discriminated against is that you are trying to stop subtle put-downs directed towards people who write mostly understandable posts, but with minor flaws that often come with not being a native speaker. The worst interpretation is that this is Stack Overflow (the company) once again trying to lower the standards (in a top-down way) so that anyone can participate and not feel left out.
Either way, it seems like this is an unnecessary element in the Code of Conduct since subtle put-downs based on language fluency are already disallowed and discrimination based on whether people can communicate is necessary on every Stack Exchange site.