I can usually tell the difference between people who are
a) not fluent in English
b) reasonably fluent in English, but
being lazy, and/or
using the language barrier as an excuse to be arrogant or rude, and/or
purposely using absurd writing styles (e.g., 13375p33k
c) simply cannot from coherent thoughts, in their native tongue or otherwise.
In any case, I'd agree that English should be used in all conversations on Dynamic Drive.
As John hinted at, this wouldn't be meant to exclude anyone, but to be as inclusive as possible. I would encourage anyone who is multilingual to help out and translate (post in both languages) for anyone with a legitimate language barrier.