I’ve found that ch and ex units are heavily influenced by latin characters. They just give weird results with non-latin characters leading to magic numbers. But the concept is really solid: use them if you want the spacing relative to text.

This is a problem whenever someone outside a culture tries to design for that culture. I have just enough knowledge of say, CJK+Arabic to read them, but not enough to know if the font/kerning/justification I'm using is attractive or ugly to natives.

It's often easy to spot Chinese goods because English writing on the stickers or manuals is in that horribly ugly latin serif font with bad kerning, which almost certainly looks fine if you don't read English all day.

Thought a magic number is when you hard code a number in logic instead of pulling from a data source

Nobody uses ch, let's be honest.