"Everyone" who speaks a Western European language, perhaps; and even
then, mostly because a lot of tools still have a "oh, it's not valid
UTF-8, guess iso-8859-1" mode. The most common instance of non-ASCII
characters in Linux kernel code are people's names, and there are plenty
of names which aren't representable in either ASCII or iso-8859-1.
The debate on this was years ago, and the consensus was to migrate to
UTF-8; however, the salient information should be expressed in the ASCII
character set unless impossible.
-hpa
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