Hi Nemo,
Do you literally want the ISO-639-3 code even where MediaWiki and Wikimedia use the ISO-639-1 code? If so, what for?
We work on an international dictionary for nautical terms. ISO 639-3 is the international code used for software. I need the relation between ISO 639-3 and WP-shortcuts, because we think about integration to WD/WP.
see https://meta.wikimedia.org/wiki/Special_language_codes for the few inconsistent codes.
Thanks! Markus