In our unit tests we set the locale to be German to get a consistent output between Windows and Linux builds. We figured out that in Windows the year has 4 digits and on Linux it hast 2 digits.

Digging into this I always thought that this was due to Linux but I figured out that Qt just does not seem to take the installed locale into account.

On my system (Ubuntu 23.04) the locale de_DE says

% Appropriate date representation (%x)

d_fmt   "%d.%m.%Y"
 

which should be the same as on Windows (4 digits).

Interestingly my KDE5 desktop also shows the date in 2 digits.

A good workaround would be if it was possible to specify the date format of a QLocale programmatically (eg. a setter method). This would also be very helpful for our unit tests.