There's something very odd about the way this is implemented. I've just been through this again after an in-place upgrade, and decided in future I'll just leave it as US and give up.

It's possibly even related to the order in which you make the several changes necessary to achieve your language configuration. So even if with a combination of display language, locale, speech language and probably sthg I've forgotten Cortana is finally persuaded to work, you may still get this message.

If I were to do it again, I'd do the in-place upgrade repair (or clean install) without updates, no internet connection, then make a disk image and create a restore point, then attempt the language settings changes with those fall-backs, and then reconnect the internet.

MS has made this really awkward and unreliable (in my opinion). It has become a matter of trial and error, until someone works out a completely reliable sequence.