I think the reason why all sites are in English is because English is the language that most of the people are understanding. You could open this question for any other language in the world and it would always be the same answer.
You can not support more languages than one, because if you would do so, people would ask Questions in many different languages and the idea of the stackexchange networks would get lost.
Imagine you are asking about something specific in Arabic for example about Computer Networking and none of the Arabic guys knows the answer, but someone from New York knows it, but he cant tell you the solution because... Well he does not know what you are asking.
But I totally get your point and could imagine a possible solution, which would look like this:
The stackexchange buttons and links get translated in lets say the 10 most spoken languages in the world.
There must be a new Create Question Dialogue, where you can choose in which language(s) you are asking.
So lets say you have chosen Arabic, then you write down your Question.
The people who have chosen Arabic in there preferences will see your question and can answer it (or not)
If you have chosen 2 languages, for example Arabic and French, then only the people who have chosen Arabic or French in there preferences will see it and will answer it (or not).
Once you got the answer, you accept and the French and the Arabic Question are marked as accepted.
I see many downsides for that concept and it would need to be improved a lot,
right now I am lacking in time and cant work out a better concept yet but maybe someone else got more thoughts on that.