I've been working on a paper (attached) for WG14 that I also intend to
submit to WG21 (with C++-specific wording) and am looking for some
early feedback from SG16 as the topic relates to text encoding of
diagnostic messages.

The basic thrust of the paper is that both languages have constructs
which can produce diagnostics including user-defined text and don't
have a "compiler diagnostic character set" defined to convert the text
into. So the paper tries to limit the damage by allowing characters
outside of the basic source character set to be handled as a matter of
QoI. The paper also asks a question that Tom H posed to me, which is
whether we want the restriction to be against the basic execution
character set for slightly easier handling of \r and \n.

Any feedback you feel like providing is appreciated. Thanks!

~Aaron