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-desktop 's PO files:

gettext: po/tok/plasma_applet_org.kde.plasma.kickoff.po: tok not a language code
gettext: po/tok/plasma_shell_org.kde.plasma.desktop.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.