[HKH2]

I can't read Japanese. I just know they use characters slightly differently, so I can't be sure they wouldn't write that.

The majority of people in the world can read and type 'S' easily, not so for '小'.

It seems you're basically arguing for pictograms. Like coding in Wingdings with a character map or something.

I would prefer to use a number scale, but if I had to choose from those options I would use whatever is most conventional in whatever area I'm in, which would probably be XXS.