Comment 2 for bug 932030

I've pushed a commit to git master for this: http://commits.kde.org/muon/5761a87fcb8cab15ca425019bc5ca22a5df809d1

It uses the check-language-support utility from language-selector, just like aptdaemon does. Both the Muon Software Center and Muon Discover use this, but the Muon Package Manager will stick to the default marking that apt does.