Linking between sister projects is very much encouraged where it is appropriate. For instance, if Wikipedia has an article about a term that is also defined on Wiktionary, links to the other should be included in both. Quotes from a famous figure who is also the subject of a Wikipedia article may appear on Wikiquote, or a how-to book about an article topic may be on Wikibooks. Article topics may also first appear on another project besides Wikipedia: A current event covered on Wikinews might well evolve into a Wikipedia article. Like interlanguage links, these interwiki links should only be made to existing articles on an equivalent topic.
Also, like links between different-language versions of the same project, interwiki links between projects use special codes to identify the project. These codes were given in the boxes included in the previous section describing the individual projects; they are commons, wikt, b, s, q, wikispecies, and v. These prefixes can be combined with language codes to produce a double prefix using a consistent naming scheme: For example, de:wikt: is the double prefix referring to the German-language Wiktionary.
You can link between Wikimedia projects in two ways. The first is to use regular in-text links, with full or abbreviated names, similar to interlanguage links.
These standard links may simply take the form
[[nameofproject:nameofpage]]where nameofproject is the name of the Wikimedia project you wish to link to (Wikipedia, Wikiversity, Commons, and so on) and nameofpage is the page title that you wish to link to on that page. This is simple and intuitive enough: [[Wikiquote:Lord Byron]] is the page for quotes relating to Lord Byron. Notice that no indicator is included about which language version of Wikiquote you are linking to; if you don't specify a language, the link will go to the equivalent project in the same language you're linking from. For instance, if you include the Lord Byron link on the English-language Wikipedia, clicking it will take you to the English-language Wikiquote page for Lord Byron. After all, most of the time that would be what you wanted to achieve.
The name of the project may also be abbreviated in a shortcut form, as mentioned previously. Because the shortcut form for Wikipedia is simply w, you can link to a page on Wikipedia from another project with a link that looks like this:
[[w:nameofpage]]If you want to link to another language edition of another project, use the double prefix—the project code with the language code, with a colon in front of it. For instance,
[[:es:wikt:fish]]
will take you from any project to the Spanish-language Wiktionary entry called fish, which in this case contains a Spanish explanation of the English word and a link to the Spanish equivalent—pez. The colon convention is required for the same reasons we explained in Chapter 15: No colon means a link is moved onto the sidebar as an interlanguage link.
These links may be piped as for conventional wikilinks, so for instance, you could set the link to read like this:
[[w:nameofpage|read more about this on Wikipedia]]Defined shortcuts, which we have listed project by project, are also detailed with those for some other sites on [[Wikipedia:Interwikimedia links]].
The second way to link to a sister project is to use one of the special templates that have been set up for this purpose. On Wikipedia, this is the preferred way to provide such links. The advantage of using a template is that the resulting link is set apart in a box with the logo of the project being linked to and some explanatory text. You will generally see these templates at the bottom of articles when they are included, in the Further reading or External links section, though they can appear anywhere throughout an article; for instance, a template linking to Wikiquote may appear in the Quotes section of a Wikipedia article.
These templates are detailed at [[Wikipedia:Sister projects]]. Except for a few special ones, they link to a search for the parameter name (usually an article name) that you type, rather than to the page with that exact title directly; that way, if no title matches are found on the sister project, full-text matches will be displayed instead.
Wikipedia has individual templates to link to all of the sister projects. A separate template for linking to all of the projects at once is also available and can be used for a very common topic that may have an article on Wikipedia, a definition on Wiktionary, media on Commons, a text referring to it on Wikibooks or Wikiversity, and so on. This template is located at [[Template:Sisterlinks]]. To use it, place it on a page with a single parameter that is the page name you want to search on (typically the same as the article name):
{{sisterlinks|energy}}This results in an infobox (Figure 16-12) with links to search for the term energy in Wiktionary, Wikibooks, Commons, Wikinews, Wikiquote, and Wikiversity.
The individual templates for linking between projects are fairly intuitive. All should be used with the name of the page being linked to as a parameter. The templates are as follows:
{{Wikipedia}}
{{Wiktionary}}
{{Wikinews}}
{{Wikibooks}}
{{Wikiquote}}
{{Wikisource}}
{{Wikispecies}}
{{Wikiversity}}
{{Commons}}You can use
{{MediaWiki}}
{{Meta}}for linking to the MediaWiki wiki and Meta-Wiki. These last two are primarily helpful for linking cross-project help pages and documentation.
Note that the Wikipedia template is not necessary (and, in fact, just won't work) when linking from one language version Wikipedia to another; using the language code is sufficient. Many variations of these templates exist for linking to categories on other projects; you can find all of the templates at [[Category:Interwiki link templates]].
Occasionally, a page will be added to Wikipedia that doesn't belong but would be appropriate for one of the sister projects. For instance, a dictionary definition doesn't belong on Wikipedia—but would be great at Wiktionary. These pages are candidates for being copied to another project. The jargon transwiki applies to moves of material from one wiki to another. The term is appropriate for pages from any namespace that need to be moved to another Wikimedia project; for instance, technical help pages might need to be transwikied to MediaWiki, whereas Foundation-wide pages might need to be moved to the Meta site.
Pages that need to be moved can be marked with transwiki templates; these work like other templates and can be found at [[Category:Transwiki templates]]. These templates mark the pages for automatic moving to other projects.