The following rules apply:
- links like this are possible ("Main Page" and "de:" are just examples):
- en:Main Page, de:Hauptseite, etc. - language version of Wikipedia, unless the link is from a Wiktionary or Wikiquote, then the language version of that set of projects; this works for all existing Wikipedias (list of codes) and Wiktionaries and Wikiquotes (same list, but not for all languages a Wikiquote exists yet)
- w:Main Page - English Wikipedia
- w:de:Hauptseite - German Wikipedia (also from a Wiktionary or Wikiquote)
- wiktionary:Main Page - English Wiktionary
- wiktionary:de:Hauptseite - German Wiktionary
- wikiquote:Main Page - English Wikiquote
- wikiquote:de:Hauptseite - German Wikiquote
- m:Main Page - Meta
- wikibooks:Main Page - Wikibooks
- wikisource:Main Page (works from Meta; from en:, oddly, one has to use m:wikisource:Main Page)
- a prefix that is "superfluous", because it refers to the same project, is allowed in the case of the prefix en:, de:, etc., w:, and m:, but not for the prefixes wiktionary:, wikibooks:, and wikiquote (in the project itself the last three are taken as namespace prefixes)
- as demonstrated above by the double prefixes, links may cumulate, thus enabling links that are not possible with a single prefix:
- links from a Wiktionary or Wikiquote to a Wikipedia other than the English one go through the English Wikipedia
- links from a Wikipedia to a Wiktionary or Wikiquote other than the English one go through the English Wiktionary
- links from a Wikipedia to Wikisource go through Meta
Prefixed internal link style is also possible for links to various wikis and some other sites outside Wikimedia, e.g. Wiki:WelcomeVisitors and MeatBall:MeatballWiki, and Google:searchterm. A list of sites is at , see also Interwiki map and en:Interwiki.
A prefix other than w:, wiktionary:, wikiquote:, m:, wikibooks, a valid language code, or a valid code for an external wiki, is treated as an internal link: a namespace prefix or just the first part of the name of a page in the main namespace.
The simplest interwiki links consist of the prefix only; they lead to the main page.
Only links within a project may show as broken, leading to the edit page. Existence is not shown for links to pages of other projects, until the link is applied.
A link of the first type in the list above (en:, de:, etc.) from a Wikipedia to another one, from a Wiktionary to another one, or from a Wikiquote to another one, is treated differently unless it is on a talk page of any namespace: as a special interlanguage link, appearing at one or two edges of the webpage (in Monobook on the left, in Classic at the top and bottom); to make it inline, prefix a colon.
The link label can not be controlled, it is the name of the language in that language. The target is only shown in the hover box and the status bar, depending on the browser.
Therefore this kind of link is mainly suitable for linking to the corresponding page in another language, and not very suitable for multiple links to the same other language. Currently only the first such link in a page is shown in the sidebar. See also Interlanguage use case for a discussion of common troubles with this system and other possible implementations.
The feature can also be used on an image description page, to link to the same or a similar image in a sister project. Other interwiki links to images require the prefixed colon.
Note that a page that might be used as a template, even if it is in an other than the template namespace, is not very suitable for an interlanguage link: such a link appears in the edge of the page that includes the template, giving the impression that the link is to a version in the other language of the referring page instead of the template.
The list of language codes for which this feature applies, including languages which have no Wikipedia, Wiktionary and Wikiquote yet, but for which the feature potentially applies, i.e. applies after the wiki has been created, with local and English name of the language, is Names.php.
The languages that have a Wikipedia and (possibly empty) Wiktionary that are not on the list (commented out) are Klingon (artificial) and Serbocroatian (obsolete). Interwiki links to these always appear in the page body, e.g. tlh:tlhIngan Hol; see also Artificial languages equal rights.
The exceptions apply for linking to those projects, not for linking from them.
An interlanguage link in the wider sense includes what, for the software, is a regular link, also an internal one on projects which are shared by different languages: Meta, Wikibooks, Wikisource, Wikiquote, see:
- Meta:Interlanguage links
- wikibooks:Wikibooks portal
- wikiquote:Wikiquote:Other Language Wikiquotes (discussion)
Possible reasons for using an "interlanguage link" in the page body include:
- control over position
- control over label
- especially useful in the case of a page used as a template, so that on the referring page the link label can explain what the link target is.
- the target contains an anchor
Many wikis allow the prefixes WikiPedia (for the English Wikipedia) and MetaWikiPedia, which are in http://usemod.com/intermap.txt. Linking from a CamelCase-wiki (which does not use brackets for links) to a page that contains spaces in its title typically requires substitution of the spaces with underscores, e.g. WikiPedia:Main_Page. For details, refer to the wiki one wants to link from.