Localization of listings on AMO works kind of weird.
First off, when creating a new locale for a listing, the Summary and Description fields are not automatically pre-filled with the text from the default locale unless you focus the field and then unfocus it. I think that’s a bug though, so I’ve made an issue on GitHub for it.
The other bigger issue is that the default locale text isn’t properly carried over to listings that don’t have a localization for that field.
For example, let’s say my default locale is English and I already have a French locale listing. I have the email field set in the English listing. Because I’m not using locale-specific email addresses (which is likely the case for most), I have not specifically set the email for the French listing. The email for the default locale appears in the field for the French listing greyed out to indicate that it’s pulling that from the default locale.
Now, if I decide to change my email address for my listing, I change it on the English listing. However, it doesn’t change in the French listing and now appears in the French listing as plain black text as if I had filled it in myself.
So if you have a lot of locales, you would need to manually change (or clear out) the field to get the correct one to show on the other locales.
In my opinion, this should not work that way. If the listing is currently using the text from the default locale, it should automatically update when that field is changed on the default locale.