Manual:$wgEnableScaryTranscluding

Details
Enable scary transclusion (transcluding pages or templates from another wiki). Reasons for its somewhat strange name: It's scarily inefficient. See User:Peter17/Reasonably efficient interwiki transclusion for a better, but currently (September 2010) not yet stable approach.

This setting applies only to pages in the template: namespace; both $wgEnableScaryTranscluding and the iw_trans bit in the interwiki table must be set for this to be enabled.