Manual:Page customizations
From MediaWiki.org
[edit] Page customizations
These are pages not existing in vanilla MediaWiki which interface definition files (in any language) expect to exist. If you want to avoid broken links in the interface you may want to make sure that either they contain some helpful content or redirect/customize them to appropriate pages (either via redirects at the pages or via editing the pages definitions).
The page names are held in pages in the MediaWiki namespace, so you can host the pages in a different location by editing the appropriate message.
Here are the referenced pages in a default MediaWiki installation (not all of them used on MW.org, hence some red links).
On your local System messages special page you can search for interface strings using these page definitions.
