Comment 20 for bug 162196

I am no IPP protocol expert but I found the following
which might be perhaps of interest for you:

See RFC 2911 section 3.1.4
---------------------------------------------------
The "attributes-charset" attribute MUST be the first
attribute in the group and the "attributes-natural-language"
attribute MUST be the second attribute in the group.
In other words, these attributes MUST be supplied
in every IPP request
---------------------------------------------------
and sub-section 3.1.4.1
---------------------------------------------------
All clients and IPP objects MUST support the 'utf-8' charset
[RFC2279] and MAY support additional charsets provided that
they are registered with IANA [IANA-CS]. If the Printer object
does not support the client supplied charset value, the Printer
object MUST reject the request, set the "attributes-charset" to
'utf-8' in the response, and return the 'client-error-charset-
not-supported' status code
---------------------------------------------------

Here the client-error-charset-not-supported status code
is mentioned while the cupsd returns a client-error-bad-request
so that the above is perhaps not the exact right part of
the IPP specification but I hope it points at least into the
right direction.

Does HPLIP explicitely set the attributes-charset
to utf-8 in every IPP request?

By the way. see also my question
https://answers.launchpad.net/hplip/+question/35351