macOS, iOS and Android all get this wrong, insisting on "correcting" color to colour. This happens in both native and web apps. I tried to work around this by adding English (US) as a secondary language, which fixes the issue in iOS but not macOS or Android.
A couple of other related points: it's irritating when apps don't use my location to pick sane defaults. Google Maps on a new phone showed me a distance in miles. A computer should never ask you a question it can work out the answer to. If you still want to change it, fine, but the default should be sane.
Another problem with language is that many developers think of I18N as a checklist item to be ticked off. They still use American English like "way to go". Leave the Americanisms out of it, if you want your non-American users to feel welcome, as opposed to, "This isn't for you". Americans will also understand if "way to go" was replaced by "congrats" or "congratulations".