And to be practical, that's fine. In a big codebase it's more important to encourage consistent, well-defined, small interfaces, and a clean separation of concerns, than to try to get consistency in the lower-level implementation details. Other non-code concerns like coordinating releases and migration of shared services are also way more important than getting everyone to use the same string library.

(Of course, if you carry that principle to the extreme you end up with a lot of black-box networked microservices.)