Yes and no - but your point is great in general. I think that there are cases where we who are fluent in English just overestimate the English skills of some people and countries.

While internationalization is not always preferable, as you point out, there are times where it means making a service or tool accessible to people who otherwise would not have access to it. We already know how dreadful the GitHub interface can be to newbies, not to mention the English language itself.

GitHub is such an important tool to developers and entrepreneurs that we should think very carefully about barring other people from using it inadvertently.

Internationalization will have adverse effects, definitely, but I still think the discussion of whether making GitHub English-only is worth deterring people who may not otherwise find their way into software development, programming, and the like. Just think of the many other ways people are starting to use GitHub.

But I for one dread the day I receive unsolicited Pull Requests in Russian for an undiscovered 0day vulnerability. :)