site_data_dir() returns '/usr/share/plasma', which is a directory of KDE Plasma. Expected would be e.g. '/usr/share' or '/usr/local/share/'. This is because site_data_dir uses $XDG_DATA_DIRS which at least under Kubuntu 18.10 is '/usr/share/plasma:/usr/local/share:/usr/share:/var/lib/snapd/desktop'.