Since being able to ask difficult, technical questions in your native language would make it easier to learn, I don't see what's so bad about that. Yes, it fragments the community, but it also recognizes that the world is not English only. Right now there's large Chinese, Russian, Japanese, and French communities that are second-class citizens without a tool like Stack Overflow.
For example, a "stack" or a "filter" or a "queue" all have specific meanings outside of programming, their nature hints at how they work, even if the technical meaning is obviously different.
Not knowing what any of the things were leaves you with a hazy concept of what they are until you understand their English analog.
I still think it makes sense to try and explain concepts in the language in which one is most proficient, then worry about English later.
That's how I played all games as a kid :) Civilisation + dictionary FTW
It's more difficult to try to learn one ignoring the other IMO. I had collegues that didn't care much for english, but it was surprising how good they were at parsing other people's code and understand how libraries and APIs worked with very few hints.
And that is the whole point of this article; there already is a lot of programming culture that we simply don't know about because those people don't hang out on HN. They deserve a StackOverflow, too :)
In most of Latin America, English lessons are not something important for most people, because the actual chance to go abroad for work and actually speak the language is non existent. And that has to do with the nature of the jobs here. Having said that, I've notice that at least in Chile, and particularly in the startup/software development sector, this is changing at very quick steps, I'd presume it's the same in the rest of Latin America.
So, it's only natural that we have one language for programming, and don't think is a bad thing, quite the opposite. As a social measure, SO is hitting the jackpot, giving spaces for those who didn't have any.
I, personally, would focus more in teaching real life English, i.e. speaking the damn thing in the first place, focus on real life situations, and what not. SO should think this measure is only a patch, in some form. Is not, and it shouldn't be think of as a solution.
So on the one hand if the culture of programming is in English (is it?) then I would strongly encourage anyone wanting to program to learn English. On the other hand, helping inject a programming environment into another language seems a worthy goal as well. On balance it seems like stackoverflow is doing the right thing.