I saw this post on Area 51, spurring me to request that SO and perhaps the rest of the SE sites be "localized". However, this would lead to an additional requirement: Anyone using SO would need to have a language associated with their account. They would also have the option to view results in only their language.
Being an iOS developer, I would suggest that the developers of SO follow the model used by Apple in iOS to localize strings, thus making it easier for users to contribute to localizations. (Use placeholder strings in the main site and load a strings file for each language.)
Also, allow people to translate questions and mark them as such. Answers should also have translations.