I used to get a lot of Korean spam, plus there's Japanese, Chinese, Cyrilic (russian) etc. All these have special charcter mapping and if you actually open the message your machine will start prompting to select languages.

Just bin them, or use a fliter that traps some of the special characters and kills on sight.

I'm trying to get the message across to my ISP's that if they don't stop spam at source (or at least in transit) they will lose me as a customer. I changed ISP recently over this and other issues.

An ISP that doesn't fight spam is a friend of spammers, and that's the last thing I need! You cannot be neutral here, especially if you're charging people for volume and therefore profiting from delivering spam.