Manual:$wgLocalInterwikis

Details
Array for multiple   values, in case there are several interwiki>Special:MyLanguage/Manual:Interwiki|interwiki prefixes that point to the current wiki. If   is set, its value is prepended to this array, for backwards compatibility (until MW 1.34.x).

Example
The setting to this configuration parameter for a wiki at  which is being liked to with the interwiki prefixes 'test', 'foo' and 'bar':

In case only 'test' is used as an interwiki prefix: