The Locale field in the Information should refresh the UI after a change

It can change the language of the UI (a current limitation) but right now you only get to see the change after a page refresh

I can't reproduce this, at least not after my latest changes. Changing the locale of the default page translation (from the Information tab) doesn't update the UI locale. When I navigate to a different page (e.g. using the Navigation tree) after changing the default locale the UI language stays the same (e.g. the UI was in English, I changed the default language of a page to French and then navigated away to a different page: the UI remained in English).

It can add a "Original Locale" field but it needs a refresh to be updated

No, this shouldn't happen, because ATM we can only change the locale of the default page translation. Whatever value we select, it still remains the default page translation, for which we don't show the "Original Locale" field (we show only the "Locale" field).

It can not change the Locale field but the user cannot realize this without a refresh, see XWIKI-23469

Can't happen anymore after XWIKI-23469 was fixed.

So ATM I don't see the need to reload the page after changing the default locale. Moreover, reloading the page requires a confirmation from the user to prevent data loss. I'm lowering the priority for now, but this could even be closed as Won't Fix / Invalid.