In r96489, maintenance scripts dumpInterwiki & rebuildInterwiki were moved out of core (clear_interwiki_cache.php is still in core). Since they were Wikimedia-specific, it wasn't really useful to generate an interwiki cache for a normal MediaWiki wiki. But it was at least more or less possible. Now it is impossible to generate an interwiki cache.
See: https://www.mediawiki.org/wiki/Manual:$wgInterwikiCache & includes/interwiki/Interwiki.php
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=30847 (T32847)