Install scalable icons & fix name of yast-yast-language.* to yast-language.*

gnome-shell very much prefers scalable icons (*.svg) for good results (sharp icons), and, as we already have them, let's install them.

the icon for language is referenced as yast-language in the .desktop file.. so either there it's wrong or the icon file names are wrong... one must change

Little typo: `256x256`