I think we have slightly different ideas about the language core vs. library distinction. In C, for example, printf and strlen are library functions (stdio.h and string.h), while structs are part of the core language.

All the language core needs for Unicode is reasonable support for tagging string literals (i.e., U"blah") and a binary-safe string type. It's best if there's either a standard or de facto community standard library for doing Unicode string ops, but it doesn't need core support anymore than the Linux kernel needs to know about parsing HTTP.