Many of the utils, such as sort, aren't locale-aware. Considering that most of the world do not use English/ASCII, do you still consider that an irrelevant edge case?
I don't consider it irrelevant, but neither does uutils. However, it's also not something that is currently at a zero. I'm not even sure that this percentage of tests is related to locale support specifically. I'm sure parity will be reached here.
For example, sort has an open PR on it right now.