UAX #29 is insufficient: at the very least, you must depend on collation too.
In Norwegian, “æ” is a letter, so I believe (as a non-speaker) that they would reverse “blåbærene” to “eneræbålb”; but in English, it’s a ligature representing the diphthong “ae”, and if asked to reverse “æsthetic” I would certainly write “citehtsea” and consider “citehtsæ” to be wrong. (And I enjoy writing the ligature; I fairly consistently write and type æsthetic rather than aesthetic, though I only write encyclopædia instead of encyclopaedia when I’m in a particular sort of mood.)
In Dutch, the digraph “ij” is sometimes considered a ligature and sometimes a letter; as a non-speaker, I don’t know whether natives would say that it should be treated as an atom in reversing or not.
And not all languages will have the concept of reversing even letters, let alone other things. Face it: in English we have the concept of reversing things, but it just doesn’t work the same way in other languages. Sure, UAX #29 defines something that happens to be a good heuristic for reversing, but it doesn’t define reversing, and in the grand scheme of things reversing grapheme-wise is still Wrong. “Reversing a string” is just not a globally meaningful concept.
Another person here has cited Cherokee transliteration, where one extended grapheme cluster turns into multiple English letters. You can apply this to translation in general, but also even keep it inside English and ask: what are we reversing? Letters? Phonemes? Syllables? Words? There are plenty of possibilities which are used in different contexts (and it’s mostly in puzzles, frankly, not general day-to-day life).
The concept of grapheme clusters is acknowledged as approximate. Collations are acknowledged as approximate. Reversing would be even more approximate.
Interesting addendum on the matter of reversing “æsthetic”: I asked my parents what they reckoned, and they both went the other way, reckoning that if you wrote æ in the initial word it should stay æ; my dad said he wouldn’t write it that way in the first place, but that if you’ve written it that way you were treating æ as a letter more than just a way of drawing a certain pair of letters. In declaring otherwise, I was using the linguistic approach, which acknowledges æ as a ligature of the ae diphthong from Latin, being purely stylistic and not semantic. And so we see still more how these things are approximations and subjective.
In Norwegian, “æ” is a letter, so I believe (as a non-speaker) that they would reverse “blåbærene” to “eneræbålb”; but in English, it’s a ligature representing the diphthong “ae”, and if asked to reverse “æsthetic” I would certainly write “citehtsea” and consider “citehtsæ” to be wrong. (And I enjoy writing the ligature; I fairly consistently write and type æsthetic rather than aesthetic, though I only write encyclopædia instead of encyclopaedia when I’m in a particular sort of mood.)
In Dutch, the digraph “ij” is sometimes considered a ligature and sometimes a letter; as a non-speaker, I don’t know whether natives would say that it should be treated as an atom in reversing or not.
And not all languages will have the concept of reversing even letters, let alone other things. Face it: in English we have the concept of reversing things, but it just doesn’t work the same way in other languages. Sure, UAX #29 defines something that happens to be a good heuristic for reversing, but it doesn’t define reversing, and in the grand scheme of things reversing grapheme-wise is still Wrong. “Reversing a string” is just not a globally meaningful concept.
Another person here has cited Cherokee transliteration, where one extended grapheme cluster turns into multiple English letters. You can apply this to translation in general, but also even keep it inside English and ask: what are we reversing? Letters? Phonemes? Syllables? Words? There are plenty of possibilities which are used in different contexts (and it’s mostly in puzzles, frankly, not general day-to-day life).
The concept of grapheme clusters is acknowledged as approximate. Collations are acknowledged as approximate. Reversing would be even more approximate.