When the system locale is en_DE, macOS seems to think we should use en_GB as the right translation. While that probably is a sensible choice in the absence of an en_DE translation, we should definitely use the en_DE translation if available, especially if en_GB isn't available (which lead to a fall-back to de_DE, given later entries in macOS's list). So prepend the system locale's own pcp47Name() if it (isn't the C locale and) is missing from what we would otherwise have used for uiLanguages(), after likely sub-tag perturbations. Add a test simulating (some approximation to) what macOS was doing that would have caught this case; and add a scope-guard reporter to the test to report what shows up when lists don't match. Fixes: QTBUG-104930 Pick-to: 6.4 6.4.0 6.3 6.2 5.15 Change-Id: I116234708067e1717d9157aebc84da76e04a9f38 Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>