It seems workspace 1-4 is called: 1 2 3 4 But then the workspavces after that is called: Workspace 5 Workspace 6 Workspace 7 Workspace 8 ... So i suggest having it consistent like: Workspace 1 Workspace 2 Workspace 3 Workspace 4 Workspace 5 Workspace 6 Workspace 7 Workspace 8 ... I have updated Xfce and the translations so it might have happened during that if there was already 4 workspaces in the old versions but maybe someone else can check to see what they got. Go to workspace switcher settings and add some workspaces to see if they are named consistently in the list.
Most likely a distribution specific change. For Xubuntu see: https://git.launchpad.net/xubuntu-default-settings/tree/etc/xdg/xdg-xubuntu/xfce4/xfconf/xfce-perchannel-xml/xfwm4.xml#n52
Copied to https://bugs.launchpad.net/ubuntu/+source/xubuntu-default-settings/+bug/1829778