Logically equivalent doesn't mean equivalent for computers. While you can't define why reverse of “noël“ is “lëon“ by set of rules that computer can follow, computer just can't know.
Umm. For that case you definitely can define a valid reversing algorithm. The key is using grapheme clusters as the indivisible base unit. Sure, there are probably some weird languages that will not reverse properly with such algorithm, but it would still be a significant improvement over the current situation.
