From my experience (I'm from non-en), a lot of non-en programmers can understand technical English decently well, but they cannot write it (or at least not enough to express complicated ideas). So they code with comments/issues in their local languages.

I've seen that at a number of local companies and since Github is used by companies too, it might make sense that the company can choose to have it localized.

I tend to agree for open source though : we need a lingua franca and it seems like English is the best pick for that.

In the end, maybe it should be up to the project to choose the interface language.