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 znc 's PO files:

gettext: src/po/znc.bg_BG.po: znc not a language code
gettext: src/po/znc.da_DK.po: znc not a language code
gettext: src/po/znc.de_DE.po: znc not a language code
gettext: src/po/znc.el_GR.po: znc not a language code
gettext: src/po/znc.es_ES.po: znc not a language code
gettext: src/po/znc.fr_FR.po: znc not a language code
gettext: src/po/znc.id_ID.po: znc not a language code
gettext: src/po/znc.it_IT.po: znc not a language code
gettext: src/po/znc.nl_NL.po: znc not a language code
gettext: src/po/znc.pl_PL.po: znc not a language code
gettext: src/po/znc.pt_BR.po: znc not a language code
gettext: src/po/znc.pt_PT.po: znc not a language code
gettext: src/po/znc.ro_RO.po: znc not a language code
gettext: src/po/znc.ru_RU.po: znc not a language code
gettext: src/po/znc.tr_TR.po: znc 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.