The notification like “Language support is incomplete, additional packages are required” means that not all the language packages installed all upgraded, to fix this you need to execute next command……

sudo apt install $(check-language-support -l en)

here “en” is a language code, so if you need additionally support for example for Italian language you need to run it once again, like this

sudo apt install $(check-language-support -l it)

If this notification annoying you and you don’t want to install anything, you can just disable it in

Go to System Settings > Personalization > Other Notifications and uncheck Incomplete language Support