Sorry, I keep mixing these - bytes instead of scalars, which I think would be more natural to iterate over in most languages (at least the ones I use).
You may not have seen this interesting article before: https://hsivonen.fi/string-length/. I agree with its assessment that scalars are really pretty useless as a measure, and Python and Ruby are foolish to have chased it at such expense.
But seriously, I can’t think of any other popular languages that count by scalars or code points—it’s definitely not most languages, it’s a minority, all a very specific sort of language. “Most” encompasses well-formed UTF-8 (e.g. Rust), recommended UTF-8 but it doesn’t actually care (e.g. Go), potentially ill-formed UTF-16 (e.g. JavaScript, Java, .NET), and total-mess (e.g. C, C++).