Last modified: 2012-04-16 09:15:53 UTC
Shouldn't things like de-formal, en-gb, nl-informal be added to $wgDummyLanguageCodes?
en-gb at least is a valid language code.
It looks like this bug is actually invalid and was due to incorrect documentation at Mediawiki.org. I've updated the documentation to be more accurate (http://www.mediawiki.org/wiki/Manual:$wgDummyLanguageCodes). Resolved as invalid.