Comment 10 for bug 1392699

Please note that for 5 years or so Ubuntu has provided GUIs for setting language on one hand, and the formats related locale categories as a whole on the other hand, separately. It's true that there has been no GUI for setting the various formats related locale categories independently. OTOH, I have followed the language/locale related bug reports and Ask Ubuntu questions closely for quite a while, and my impression is that few users would rate that feature high. (It's also possible to fine tune the settings by editing e.g. ~/.profile.)

It should be noted that the example in the summary of this bug report - changing 12/24-hour time and date format independently - can't be accomplished by picking the different locale categories individually anyway, since both are controlled by LC_TIME. To do that we would either need to add a feature that creates and maintains a custom locale for each user, or handle it in respective application.

As a first step, to make some progress and make it possible to fix bug #1350275, I would recommend that a GUI is added to ubuntu-system-settings for simply selecting regional formats independently from selecting the display language. As illustrated by Alexey's workaround, the backend in accountsservice for such a feature is already in place.