Inclined to agree with you about this, but isn't the post talking about localisation only for the github website UI itself .. a separate issue to the language used in comments, commit messages, code, etc. It just brings down a barrier that might be stopping some people using it.
> "If a user comes to a site that is using her primary language, she will interact with that site using that language."
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...
