Truncating text is almost always (in my experience) a UI thing, where you pass a flag to some UI widget saying 'truncate this and that on overflow' and while rendering, it can then truncate using grapheme clusters.

How often does one reverse text? And when do users care about text length? Almost always (again, in my experience) in the context of rendering - when deciding on line length or break points, so when you know and care about much more than just 'the string' - but also font, size, things you only care about in the context of displaying. Not something that should be part of the 'core' interface of a programming language.

I mean I think we agree here; my point was that I too used to think that grapheme clusters mattered, but when I started counting in my code, it turned out they didn't. Sure I can think of cases where it would theoretically would matter, but I'm talking about what do you actually use, not what do you think you will use.