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 your wiki's interface you need to either create these pages or change the messages, see Fixing pages below for more details.
Here are the messages in a default MediaWiki that reference pages (not all of them used on MW.org, hence some are red links in this table).
On your local System messages special page you can search for interface strings using these page definitions.
Fixing page edit
To fix these broken links, you (or an administrator on your wiki) can:
- Create the missing page
- Just visit it on your wiki, create it and start writing. MediaWiki.org has suitable help material you can paste or import into your wiki. You can make the page a #REDIRECT to another page.
- Link to a different page
- Edit the interface message by visiting its page in the MediaWiki: namespace and change it to a different page title, or possibly an external URL.
- Remove the link
- You can edit the message to not have a link. In some cases you need to rephrase or blank out a different interface message(s) that incorporate the interface message with the URL. For example, 'helplogin-url' is the link in 'userlogin-helplink', so if you don't wish to provide this guidance, you can blank out MediaWiki:userlogin-helplink. Since removing the text in a message resets it to the default for your language, you should blank out a message by changing it to an HTML comment such as
<!-- blank since this wiki does not currently provide login assistance -->