It works on account of Arc using the underlying MzScheme string implementation. Since this is incidental to the host and not part of the arc spec (arc.arc), it is not guaranteed to keep working.
A patch to support unicode (which PG has asked for) would have to include a "native" implementation of strings in Arc, which is a rather fundamental extension to the language, and I suspect the language designers would want to do this themselves? Or would you (the Arc language designers, if you read this) accept such a patch?
