>On a practical front, it may help implementers is there were a pair of tab
>or comma delimited files that provided mappings between RFC3066 and

See ,then follow the link "langues" (this is
an XML "flag")
(Currently, the link is not the file itself, but the CVS repository "view" :*checkout*/mods-fr/xsl/langua

This is an xml file, but i create it with Excel (cut and past from the
ISO9639-2 web page).
You could see the delimited file at the end of this email.

I could copy the Excel or CSV file on the internet.
But i think there is a better solution :
  if the loc could provide these XML files (lang, country, relators, etc.).
  Some XSL stylesheets could be used to obtain the html (normal) version,
even the csv files.

So one reliable source (XML), many final-form generated automatically, and a
lot of happy users :-)