If a user tries to add a sitelink to an item which already exists, they get this message:

Could not save due to an error.

The save has failed.

This is with an English UI. In German, we get "Die Speicherung konnte aufgrund eines Fehlers nicht ausgeführt werden. The save has failed.", and in French "Échec de l’enregistrement en raison d’une erreur. The save has failed.", suggesting there are two different error messages being displayed here, since one is localised & one not.

This is quite confusing for new users, since it doesn't explain what the error is. Would it be possible to give a more user-friendly message?

For example, "Could not save due to an error: this link already exists on another item". (Listing what item it exists on which would be ideal, of course, but that would presumably be more work...)