Hi Martijn, never received an answer for this. I don't think anyone has any recollection about this subject. Perhaps somebody on the two lists "Debian Development" <debian-l10n-devel@lists.alioth.debian.org>,"Debian sproglisten" <debian-i18n@lists.debian.org> can help out?
If i take a look on http://ftp.debian.org/debian/dists/Debian7.4/main/i18n/ it looks like some languages does receive updates. Perhaps we could make a test and update e.g. Danish?
http://ftp.debian.org/debian/dists/wheezy/main/i18n/