StackOverflow in other languages is a redundancy detrimental to the global community of programmers.
A great deal of effort in the design of stackoverflow is put into detecting and eliminating redundancy, to help its users save time and effort when looking for an answer or answering a question.
What do you prefer, a great tower of Babel or hundreds of mostly overlapping replicas with a centesimal fraction of its usefulness and greatness?
As I write in Spanish, I cannot write in English.
A person who learns English has immediate access to all the existing information on the site.
Anyone can learn English. Learning English and using it as a technical language does not require more effort than learning a new programming language.
You think you're leading an effort to increase the community's scope and reach more people, but such an effort can only end up in excision.
It is an effort that harms everyone, even those who are supposed to benefit from it: As a programmer in India writes a response in Hindu that already exists in English, he or she is being kept from answering a new question. The same happens with other languages and in the end we all get a fraction of what we would have if we agreed on one language for everybody. Meanwhile a significant amount of people who grew up in an environment where the only spoken language was not a popular one would still be in great disadvantage.
In short, splitting StackOverflow in different languages is the very definition of inefficiency.
It's like when a new programming language that brings nothing new comes out, but we have to learn it because some consortium has the interest and enough power to put pressure so that it becomes another de-facto standard; not only we have to redo everything that was done in the new language if we want to collaborate with the consortium, but also new creations are not made available to the pre-existing languages until someone comes and bothers to port them, multiplying the effort we have to put by N times to achieve the exact same goal.
Today the vast majority of programmers have to learn English if they want to be competent.
I hope it stays that way for long, because although like everybody else I would also prefer the official language of the programmers to be my mother tongue, I am not willing to sacrifice a global community with the means and tools for fluid communication with the least amount of noise for a fraction (no matter how significant) of what it currently is, only to express myself more comfortably or include people who are too lazy to learn how to communicate.
And now I could move on to another topic, but I have to double my efforts and waste my time to write this in Spanish to accommodate people who do not want to accommodate to what luckily is a universally accepted standard: English as the official technical language, not only in programming, but in all branches of engineering.
I only have one request regarding the language issue on stackoverflow and stackexchange sites: Please let the community flourish by being kind and offering your support and acceptance to those like me who are still learning the language and putting their best effort on improving their communication skills to be as close as possible to the rest of the community. If we give them the proper encouraging we will all end up benefiting from those who are still shredding the language but have or will have great questions and answers to contribute: If you think a question is interesting or an answer is valid but it is poorly expressed, please edit it instead of simply downvoting it.
Proposal: Stack Overflow (in Spanish)