You can check if a PO file is valid with the following command:

        msgfmt -c -o /dev/null <po file>
      

The following errors were found in plasma-workspace 's PO files:

gettext: po/tok/freespacenotifier.po: tok not a language code
gettext: po/tok/kcm_autostart.po: tok not a language code
gettext: po/tok/kcm_colors.po: tok not a language code
gettext: po/tok/kcm_cursortheme.po: tok not a language code
gettext: po/tok/kcm_desktoptheme.po: tok not a language code
gettext: po/tok/kcm_feedback.po: tok not a language code
gettext: po/tok/kcm_fonts.po: tok not a language code
gettext: po/tok/kcm_icons.po: tok not a language code
gettext: po/tok/kcm_lookandfeel.po: tok not a language code
gettext: po/tok/kcm_nightlight.po: tok not a language code
gettext: po/tok/kcm_notifications.po: tok not a language code
gettext: po/tok/kcm_regionandlang.po: tok not a language code
gettext: po/tok/kcm_style.po: tok not a language code
gettext: po/tok/kcm_users.po: tok not a language code
gettext: po/tok/kcminit.po: tok not a language code
gettext: po/tok/kfontinst.po: tok not a language code
gettext: po/tok/kio_applications.po: tok not a language code
gettext: po/tok/kio_desktop.po: tok not a language code
gettext: po/tok/klipper.po: tok not a language code
gettext: po/tok/krdb.po: tok not a language code
gettext: po/tok/krunner.po: tok not a language code
gettext: po/tok/ksmserver.po: tok not a language code
gettext: po/tok/libkicker.po: tok not a language code
gettext: po/tok/libkworkspace.po: tok not a language code
gettext: po/tok/libnotificationmanager.po: tok not a language code
gettext: po/tok/phonon_kde_plugin.po: tok not a language code
gettext: po/tok/plasma_applet_org.kde.plasma.activitybar.po: tok not a language code
gettext: po/tok/plasma_applet_org.kde.plasma.analogclock.po: tok not a language code
gettext: po/tok/plasma_applet_org.kde.plasma.appmenu.po: tok not a language code
gettext: po/tok/plasma_applet_org.kde.plasma.calendar.po: tok not a language code
gettext: po/tok/plasma_applet_org.kde.plasma.clipboard.po: tok not a language code
gettext: po/tok/plasma_applet_org.kde.plasma.devicenotifier.po: tok not a language code
gettext: po/tok/plasma_applet_org.kde.plasma.digitalclock.po: tok not a language code
gettext: po/tok/plasma_applet_org.kde.plasma.icon.po: tok not a language code
gettext: po/tok/plasma_applet_org.kde.plasma.lock_logout.po: tok not a language code
gettext: po/tok/plasma_applet_org.kde.plasma.manageinputmethod.po: tok not a language code
gettext: po/tok/plasma_applet_org.kde.plasma.mediacontroller.po: tok not a language code
gettext: po/tok/plasma_applet_org.kde.plasma.notifications.po: tok not a language code
gettext: po/tok/plasma_applet_org.kde.plasma.private.systemtray.po: tok not a language code
gettext: po/tok/plasma_applet_org.kde.plasma.systemmonitor.po: tok not a language code
gettext: po/tok/plasma_containmentactions_applauncher.po: tok not a language code
gettext: po/tok/plasma_containmentactions_contextmenu.po: tok not a language code
gettext: po/tok/plasma_containmentactions_switchwindow.po: tok not a language code
gettext: po/tok/plasma_engine_applicationjobs.po: tok not a language code
gettext: po/tok/plasma_engine_notifications.po: tok not a language code
gettext: po/tok/plasma_engine_time.po: tok not a language code
gettext: po/tok/plasma_engine_weather.po: tok not a language code
gettext: po/tok/plasma_runner_appstream.po: tok not a language code
gettext: po/tok/plasma_runner_baloosearch.po: tok not a language code
gettext: po/tok/plasma_runner_bookmarksrunner.po: tok not a language code
gettext: po/tok/plasma_runner_calculatorrunner.po: tok not a language code
gettext: po/tok/plasma_runner_kill.po: tok not a language code
gettext: po/tok/plasma_runner_locations.po: tok not a language code
gettext: po/tok/plasma_runner_placesrunner.po: tok not a language code
gettext: po/tok/plasma_runner_recentdocuments.po: tok not a language code
gettext: po/tok/plasma_runner_services.po: tok not a language code
gettext: po/tok/plasma_runner_sessions.po: tok not a language code
gettext: po/tok/plasma_runner_shell.po: tok not a language code
gettext: po/tok/plasma_runner_webshortcuts.po: tok not a language code
gettext: po/tok/plasmashell.po: tok not a language code
gettext: po/tok/plasmashellprivateplugin.po: tok not a language code
gettext: po/tok/soliduiserver.po: tok not a language code
      

Please ask the translator (identified by the Last-Translator field in the PO file), the language team (identified by the Language-Team field) or debian-i18n for a fix.