Make a dictionary called "No Oriental Character Set" (or whatever)
Set it to search the 'header' of the email/extracted text
Add in the character sets from the emails in languages you want stopped
eg. for Chinese you would add
I set a similar rule to just big5 and gb2312 some time back, not sure why I took out the "charset=" part. Maybe Ironmail had an issue with it at some point.
Looks like a complete list of character sets here:http://a4esl.org/c/charset.html
Setup the actions and apply the rule appropriately.