Filtering on character set in KMail

Steven Friedrich <[email protected]>
Newsgroups gmane.comp.kde.users.pim
Message-ID <[email protected]>
I'm running KDE 4.3.4 on FreeBSD 7.2-RELEASE, though it doesn't matter for 
this question.

I receive quite a bit of SPAM that is not in English.

One tip of the day states that you can filter on Content-type, but I don't see 
that in standard filters.

How can I filter messages that are not in my char set?
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