In systemsettings -> translations, one can select "preferred" languages from "available" languages. It would be most natural to have the option to install new languages from here. Reproducible: Always
*** Bug 28442 has been marked as a duplicate of this bug. ***
*** Bug 414898 has been marked as a duplicate of this bug. ***
You can install fonts, translation package from Region & Language KCM on Ubuntu based distro. For other distros, there is no way for KCM to query the required packages.