I'm not sure strings are easier. When to use mutable vs. immutable strings has a significant performance impact, how do you manage memory for them (including when do you copy strings vs work with a slice) are all questions where there's at least 3-4 distinct designs that you might want (a C like language, a C++-like language, a Rust-like language, and a GC'd language).

In contrast, for dates and times, everyone really could have used the same design. Maybe you'd need a slightly different design for dynamic languages, but I'm not even sure about that.