If a user comes to a site that is using her primary language, she will interact with that site using that language. That is very much not desirable at a site like Github.
Other than that, the suggestions listed sound nice to me.
This will not change any soon, and (I know it's controversial) but for the good of the devs-to-be, let GitHub remain non-localized.
I always feel the chill when someone pastes a non-English screenshot in places like StackOverflow. Or whenever I want to help some fellow dev in my company who happens to have installed Italian or French version of Firefox/Chrome/etc.!
Eventually someone replied asking for them to re-submit an English description of the issue, hopefully they're able to do so. :-/
If you can't speak english, you can't program for sure. I work with some people who are not very good english speakers. I can see it in their code. Sometimes its a mix of english and their own language. Very bad. NO-HIRE
I speak three languages, Swedish is not one of them. That was an awful summer.
If the website UI is in their native language, people would most likely also make the READMEs, issues, comments and other things in their native languages. Commit messages might also be affected, since the user would perhaps not give it much thought that they are using their native language...