Add an address field for one location only

[ikran]

Good morning, I would like to add a custom field which however remains visible only to one location.

I saw that by going to International->Location and clicking on the country concerned, a window opens with various items, including the choice of address format with the choice of fields that must make up the address.
How should I add a custom field here so as to activate it only for the desired location?

Thank you all.