When I said rot13 isn't defined outside of a certain set, I meant it. If you want ø to be half-rotatable, you need to specify an ordered character set (with an even set size) and say that rot29 or rot128 or whatever you come up with is the analogous mapping to rot13.

Now, rot13 excludes punctuation and keeps capitalization after transform, so an ordinary human can learn to read rot13 English reasonably fluently. I don't know if that is common across all Latin-descended alphabetic languages, but it's really not going to be a plausible skill in Mandarin.

https://en.wikipedia.org/wiki/Chinese_characters#Indexing is somewhere between horrifying and fascinating.

On the other hand, Korean (Hangul) has a perfectly reasonable alphabetic set size and ordering, at least in South Korea. https://en.wikipedia.org/wiki/Hangul#Alphabetic_order -- so I expect that Koreans can learn to read rot12.