MacOS – Changing the system language globally

This problem seems to crop up occasionally, and I haven't heard a definitive solution outside of the standard troubleshooting routines: determine if the problem is a software setting by creating a new user account, rebuild permissions, and so on.

Beyond the basics, there are two solutions that might help. First, in this thread over at the Apple discussion forums, someone has a similar problem and is able to resolve it by removing some spurious login items, then logging out and logging back in. It's worth looking at your login items suspiciously.

Second, you might try to change the system language to something new, like French. Log out and back in, then change back to English. It may be that you have some wonky settings left over from an old program, and that switching away from English and back re-aligns everything.

As of at least iOS 8 you can change the order of languages in Settings > General > Language and Region under the heading Preferred Language Order.