What is the best way to internationalize Schematron error messages?

Question

In your opinion, what is the best way to internationalize Schematron error messages? I don't want to duplicate the schematron files, just the assert and report messages.

Answer 1

I stumbled across this in the schematron ISO standard document:

Diagnostics in multiple languages may be supported 
by using a different diagnostic element for each language, 
with the appropriate xml:lang language attribute, 
and referencing all the unique identifiers of the diagnostic elements 
in the diagnostics attribute of the assertion. 
Annex G gives a simple example of a multi-lingual schema.

Annex G:

<sch:schema xmlns:sch="http://purl.oclc.org/dsdl/schematron"
    xml:lang="en" >
    <sch:title>Example of Multi-Lingual Schema</sch:title>
    <sch:pattern>
        <sch:rule context="dog">
            <sch:assert test="bone" diagnostics="d1 d2">
    A dog should have a bone.
            </sch:assert>
        </sch:rule>
    </sch:pattern>
    <sch:diagnostics>
        <sch:diagnostic id="d1" xml:lang="en">
    A dog should have a bone.
        </sch:diagnostic>
        <sch:diagnostic id="d2" xml:lang="de">
    Ein Hund sollte ein Bein haben.
        </sch:diagnostic>
    </sch:diagnostics>
</sch:schema>