Thank you Ira for clarifying how we intent to use 'natural-language-configured' in the 'printer:' template.
James and Erik beat me to where I was heading. As an SLP_API user, I know that a natural language must be specified with each SLP registration and request, independently of the type of service being registered/searched. It seems to me then that both SLP and IPP have already conformed with RFC 2277; SLP by requiring the natural language associated with each SLP request/query (regardless of the template being used) and IPP by supporting 'natural-language-configured' in its object model.
It would appear then that the reason for having 'natural-language-configured' and 'natural-language-supported' in the 'printer:' template is mostly for convenience, so users can get to that information without making an additional request to the printer (and as I indicated in my previous message, I question how useful that feature really is).
OK so here are some options I'd like you to consider (1 being my first choice and 3 my last):
1. Do away with both attributes 'natural-language-configured' and 'natural-language-supported' in the 'printer:' template.
2. Keep both attributes but make them optional.
3. Keep both attributes as mandatory but add 'unknown' as a legal value.