FWIW. This would probably present a challenge in most (all?) languages.

For example in libc++ due to SSO an std::string has a minimum size of 24 bytes.

For a billion strings less than 15 chars (+ the null byte) that gets you to 24GB, and that’s optimistically assuming each string is allocated in place.

I doubt heap allocated char* would do much better either. Just having a billion 8 byte pointers eats a lot of memory. You’d really need some sort of string packing scheme similar to what you did in Java.