Is this for Special:AllMessages (where link already exists) or on the message pages directly?

In T87547#4896075, @Nikerabbit wrote:

Is this for Special:AllMessages (where link already exists) or on the message pages directly?

The relevant passage is

One possibility is to allow the community of users to update the user interface in situ, either directly from the original English version or perhaps working from a less than perfect machine translation. That is, the interface would allow users to localise User Interface (UI) elements like menu-options, error messages and tool- tips as they used the tool. This localisation could be enabled via a simple pop-up micro-localisation editor that would allow them to change UI text in situ simply by ctrl-clicking on any text that is displayed. See Fig. 3.2 for an example where a ctrl-click on the ‘Options’ menu item brings a localisation editor to the fore. The user is then allowed suggest an alternative lexicon for the menu item, or to utilise other suggestions provided by the community. The localised menu-item would then become part of the application’s User Interface.