Menu order seems to use ID, not Order
I added the Croatian 'Support Us' page first to the system (because nothing was added automatically for the new language).
Then I added the other menu items.
The 'Order' value for the 'Support Us' page is higher than those of the other main menu item pages.
However, it comes first in the menu.
https://inkscape.org/hr/ ('Podrži nas' means 'Support us', and 'Develop' is the last item, highlighted in orange)