I am receiving increasing quantities of spam in Chinese, French, and other non-English languages. Does anyone know whether it is possible to create a Mail rule that applies to a specific language or character set?
Spit-ballin’ here…
If you are not receiving explicit encrypted messages, maybe set the “Message is encrypted” condition?
Perhaps (and I can’t believe I’m saying this, but…) take a sampling of the message texts and headers, feed them into ChatGPT, and ask it to make a list of words that are common to every message? (I’m sure that there would be ways to accomplish that same task, somehow, using conventional text comparison tools and regular expressions, but frankly that route just hurts my head every time I start to pursue it.)
I suppose you could always try changing your OS language to the target language, then try to navigate Mail’s rule interface in that language.
I am presuming that you are not receiving desired messages in any of these languages. If you are, then I recommend SpamSieve.
Bottom line is I don’t see an easy way to do this in Mail, but I do hope these blue-sky suggestions can prod someone’s memory or skills. 
@fellwalker57 , I just rec’d a foreign-script email into the Mail Junk folder. I viewed All Headers and found the sending email address, plainly shown in English, copied the domain part then opened Mail Settings and went to Rules, clicked Add Rule and since the email was still on display the Add Rule interface had already filled in the full from address (so I could have skipped the viewing of headers step). I set the Rule to put any email containing that domain in the Trash.
Anyway, I set the rule for the @ symbol and beyond and clicked ok. Then a window came up asking if I wanted to apply the rule now and I clicked Apply and not only the foreign script email but all email in the Junk folder went to the Trash.
Maybe that helps for your query.
David,
Yes, I have set rules in the way you describe and it works for each domain. Unfortunately, messages are coming from multiple different domains. I just wish there was a way to set a rule based on the character set used in the message.