Interlanguage links are the small navigation links that show up in the sidebar in most MediaWiki skins which connect an article with related articles in other languages within the same Wiki family. This can provide language-specific communities connected by a larger context, with all wikis on the same server or each on its own server.
For details on setting up a set of language-variations on a wiki, see Manual:Wiki family.
For examples of active wiki families using interlanguage links, see Wikipedia, Wiktionary, and Wikibooks. For an alternative method of storing pages in many languages on a single multilingual MediaWiki, see the Translate extension or, as examples, Meta-Wiki and Wikimedia Commons.