Manual:$wgImportSources

Details
Array of interwiki prefixes for wikis we'll accept as sources for Special:Import (for sysops). Since complete page history can be imported, these should be 'trusted'.

m:Help:Help m:Help:Help Interwiki Interwiki

If a user has the 'import' permission but not the 'importupload' permission, they will only be able to run imports through this transwiki interface.