If it's not going to have the syntax used in HTTP, I'd rather
have it called by some other name.
I don't think the UTF-8 requirement is reasonable.
It seems like this would impose a huge implementation burden for most UAs.
With this requirement in place, most people can't use it or benefit
from it. Without this requirement, many users could just add a header
field to outgoing mail specifying the languages and charsets that the
user can deal with, without needing UTF-8 support.
Also, the chosen I18N approach to DSNs was to define precise
error codes and include enough information so that the error
could be presented in the user's language by the user agent.
As far as I can tell, the error codes are usually adequate for this
purpose, in that they can describe most conditions with sufficient
precision. So I have to wonder if this is really needed for DSNs.
And while I could see something like this header being used for
email-based document requests, for it to affect DSNs would require
that MTAs look at the header of the subject message. This
is a layering violation.
Keith