Language-dependent stemming rules in search function on Kindle 3

[Edmundo]

Has anyone reverse-engineered this or found any official information about it?

If you search for "paren" in an English MOBI file, it doesn't find "part".
If you search for "paren" in a German MOBI file, it does find "part".
When I experimented with an Esperanto MOBI file the behaviour was weird.

So which languages does the Kindle 3 know about? And what rules does it apply? And is it possible to change the rules? And is there an official way of disabling the stemming, for example by setting the language field in the MOBI header to some special value that means "no language", "unknown language", "mixture of languages", "not a human language" or something like that?