Managing interwiki links is a basic activity that almost every new mediawiki setup has to do. For example, the predefined list of interwiki links does not contain links to language versions of wikipedia, one of the first needs for many installations.
Mediawiki core presently assumes that interwiki is being managed by SQL database statements from the command line. This is not realistic for many mediawiki installations and limits the usability of the software.
An excellent extension exists: Extension:Interwiki but is hidden among a set of similar extensions. See "review" on top of http://www.mediawiki.org/wiki/Category:Interwiki_extensions
While the review helps, a less frustrating solution would be to intergrate the extension into core.