Is this true? It was (is!) certainly true for C, but C has an especially emaciated expectation for string processing primitives. Any runtime developed after like 1995 that I can think of has fixed this by providing a sane string implementation people generally agree upon.
Rust and Go both don't have a builtin package for grapheme iteration - and many naively (and incorrectly) think that a 'Go unicode rune == "character"' in Go. I assume the same happens with Rust `char` type.
If you care about unicode-aware string sorting (you should), rather than the naive string sorting the Go and Rust standard libraries provide out of the box... then you probably want a proper Unicode library.
I think the only language that gets Unicode 'right' out of the box is Swift, as it actually provides grapheme iterators, Locale awareness, etc. - but it comes at the cost of the language being tied to the (ever-moving) Unicode standard.
I mean unicode is incredibly complex, but it doesn't even seem like there's a consensus outside of swift's string implementation of what a grapheme even is.
(Granted, this might support the above concept that people can't even agree on what a string is, but unicode code points seems like a reasonable baseline to expect from a modern language. That said, rust doesn't even include unicode normalization in the standard library, although the common crate for it seems like a reasonable solution.)
Linguistically it's easy, graphemes are the squiggles people actually draw, as distinct from how a machine encodes them. Of course since people aren't a single individual with just one consistent opinion that does mean there's room for nuance - maybe some people think this is two separate squiggles.
In recent years, application support for this has greatly improved.
I think this might (at least partially) be why Rust's stdlib doesn't have this. If it did, then support for it would be tied to Rust's release schedule and which version of Rust you're using. Granted it is every six weeks, and it's usually trivial to update, but that's still a connection that could be an issue.
By having this be in a separate library it means that it can update as and when it needs to, and it's not inherently connected to a specific release of Rust.
Let's just assume a String is UTF-8 to make things "simple".
Is a String mutable or not? Should mutable and immutable Strings have the same underlying structure? If mutable, is a String extensible or not? Can a String be sliced into another String? Can those slices be shared? Should you walk across codepoints or characters (which could be multiple codepoints due to combining)? If you want to insert a codepoint in the middle of a String, what are the performance guarantees?
I can go on and on ...
"String" really has to be a library as there are simply far too many permutations once you step away from "Shove ASCII to tty".
That said, I personally would balk at willing adopting any runtime that didn't enable iterating over a sequence of unicode code points, whether they be stored as utf8 or some 16-bit form, from a string of bytes in 2024 unless I were guaranteed to avoid having to deal with text processing of free-form human input.