Help:System message

A system message is a snippet of plain text, wiki text, CSS or Javascript that can be used to customize the behavior of MediaWiki and its appearance for each language and locale.

Special:AllMessages
Interface and other system messages can be customized by editing pages listed on Special:AllMessages. Editing interface messages is typically straightforward, just like editing a normal wiki page, but it is restricted to users with the editinterface permission, which is assigned to sysops by default.

The Special:AllMessages table contains two columns: the linked interface name, and the text. The text is horizontally split to show the default text above, and the customized text below. When a custom message does not exist, only the default will be shown. To customize a message, click the upper link in the left column (the name of the message). This link is red if the default text is in use, because the edit page is empty.

The lower links in the left column cells lead to the discussion pages for that message.

Built-in system messages
For a complete list of documented interface and system messages, please see Category:Interface messages. These pages document how each message is used by MediaWiki, variables available, parameters used, limitations, et cetera. There is more complete documentation (albeit aimed at translators, not end users) in the [//translatewiki.net/w/i.php?title=Special%3ATranslate&task=reviewall&group=core&language=qqq&limit=5000 qqq pseudo-language].

To find the message responsible for producing a particular piece of interface text in MediaWiki 1.18 and above, change to the special 'language' code qqx by appending &uselang=qqx to the URL ([ example]). All the messages will then be replaced by their message keys, so you can identify which message is responsible. In case a message is only visible whilst performing an action &uselang=qqx&debug=1 (example) needs to be appended.

In version 1.17 and below, you will need to look through Special:Allmessages for the message whose value corresponds to the text you're seeing, or to search for its text on translatewiki.net.

Creating new messages
To add new messages in MediaWiki core, the canonical language file should be edited to include the new message definition, while message documentation belongs to its file. The message should also be added to, and if it's not meant to be translated, to   too.

Extensions can (and should) define system messages for any text displayed in the user interface. This assists in the localization of those messages. For an example of how to do this, please see Manual:Special pages. If the extension is well written, it will probably be included in translatewiki.net in a few days, after its staff notices it on gerrit; if it's not noticed, contact them; if it's too instable to be translated, note so in the code or commit and contact them if necessary.

If the new message should not be translated on translatewiki.net (optional or ignored), it would need to be added to the MediaWiki/mediawiki-defines.txt file in the translatewiki Git project, see format documentation and example.