Popup: Language support is incomplete – what packages does it want to install?

I'm using Kubuntu 17.10. Always after login, the notification below pops up. When I click it, it asks for my password and wants to install or remove packages – but without telling me **what packages**. I already searched the internet but couldn't find a way to identify what packages are needed. The standard apt upgrade is not affecting this popup. What program is causing this popup, and how can I see which packages it wants to install? Thanks!