I stumbled on https://commons.wikimedia.org/w/index.php?title=Template:Cc-by-sa-4.0,3.0&uselang=nl which is a very odd template for which the i18n is not working. Looking at https://commons.wikimedia.org/wiki/Special:PrefixIndex?namespace=0&prefix=MediaWiki%3AWm-license , that's not the only case. We have:

• Messages that don't make sense and should just be removed (mostly licenses that do not exist)
• Messages that should be moved to TranslateWiki ( https://github.com/wikimedia/mediawiki-extensions-WikimediaMessages )

Maybe some other cases.

I (multichill) will probably pick this up myself (if someone else doesn't beat me to it).