i would be surprised that the filters actually support international charsets, if your PHP charset settings are not UTF-8 by default.
To use that with default PHP ISO charset, probably would need to review that line and the few other lines of code that access the storage for filter, and accept incompatibility of database storage.
I don't recall such a feature request yet, but it's something we will address in CB 2.0 latest.
In mean time try changing the php setting might be easiest.