For security reasons, not all pages inside the Media Wiki namespace are currently editable. To ensure a safe environment for Wikia's visitors, Wikia is running a security audit across all features - which means all messages must be reviewed before they can be unlocked for editing.
Below are the currently editable MediaWiki namespace pages. This list is slowly being expanded over time - if there are messages you feel should be editable as a priority, please let Wikia Staff know.
Before August 2015, Administrators and Wikia Staff members were able to edit all MediaWiki messages. However since August 2015, only Volunteer Spam Task Forces, Wikia Utilities, and later in November 2016, Wikia Helpers can edit all MediaWiki messages.
List of White-listed MediaWiki pages (including free-form messages)
List of Interface Messages that used to be white-listed
C.Syde's Wishlist for Interface Messages to be white-listed
Important Interface Messages which aren't default messages