Consider the following scenario:
1 - A user goes to meta.wikimedia.org and tries to edit the main page.
He or she gets a message reading like "This page is currently protected so that only administrators can edit it.".
2 - Then the language is changed from en-US to en-GB (British English). Then the same page is again visited.
This time, the user gets a generic error saying that "This page has been protected to prevent editing or other actions. ".
I suspect this is due to translate.wiki considering en-GB as a whole new language, but can we make messages such as these the same throughout all English 'derivatives'? The loss of fidelity, if any, should be negligible.