Sounds almost like they're building a language inside a language.
That’s not true? Python string implementation is very optimized, probably have similar performance to C.
Strings are immutable, so no efficient truncation, concatenation, or modifications of any time, you're always reallocating.
There's no native support for a view of string, so operations like iteration over windows or ranges have to allocate or throw away all the string abstractions.
By nature of how the interpreter stores objects, Strings are always going to have an extra level of indirection compared to what you can do with a language like C.
Python strings have multiple potential underlying representations, and thus have some overhead for managing and dealing with those multiple representations without exposing those details to user code
[1] - https://github.com/ashvardanian/StringZilla?tab=readme-ov-fi...
They're not building a language. They're carefully adding a newly-in-demand feature to a mature, already-built language.