Possible to hook change of url for default language

[bnomei]

maybe creating a hidden field would be a solution but its still kind of hacky imho.

Listen to certain page changes in hooks

So you need to inform this third person of both the changes that are done via the panel by the admin and the changes by team members via the custom form? For the first scenario, you can use a panel hook, for the second, you could handle this via your form processing script after the page is successfully updated?