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 kvirc 's PO files:

gettext: po/core/kvs/kvs_cs.po: kvs_cs not a language code
gettext: po/core/kvs/kvs_de.po: kvs_de not a language code
gettext: po/core/kvs/kvs_eo.po: kvs_eo not a language code
gettext: po/core/kvs/kvs_es.po: kvs_es not a language code
gettext: po/core/kvs/kvs_fi.po: kvs_fi not a language code
gettext: po/core/kvs/kvs_fr.po: kvs_fr not a language code
gettext: po/core/kvs/kvs_hr.po: kvs_hr not a language code
gettext: po/core/kvs/kvs_hu.po: kvs_hu not a language code
gettext: po/core/kvs/kvs_it.po: kvs_it not a language code
gettext: po/core/kvs/kvs_ja.po: kvs_ja not a language code
gettext: po/core/kvs/kvs_ko.po: kvs_ko not a language code
gettext: po/core/kvs/kvs_nl.po: kvs_nl not a language code
gettext: po/core/kvs/kvs_pl.po: kvs_pl not a language code
gettext: po/core/kvs/kvs_pt.po: kvs_pt not a language code
gettext: po/core/kvs/kvs_ru.po: kvs_ru not a language code
gettext: po/core/kvs/kvs_sr.po: kvs_sr not a language code
gettext: po/core/kvs/kvs_tr.po: kvs_tr not a language code
gettext: po/core/kvs/kvs_uk.po: kvs_uk not a language code
gettext: po/modules/dcc/dcc_cs.po: dcc_cs not a language code
gettext: po/modules/dcc/dcc_eo.po: dcc_eo not a language code
gettext: po/modules/dcc/dcc_ja.po: dcc_ja not a language code
gettext: po/modules/dcc/dcc_ko.po: dcc_ko not a language code
gettext: po/modules/dcc/dcc_uk.po: dcc_uk not a language code
gettext: po/modules/log/log_cs.po: log_cs not a language code
gettext: po/modules/log/log_eo.po: log_eo not a language code
gettext: po/modules/log/log_ja.po: log_ja not a language code
gettext: po/modules/log/log_ko.po: log_ko not a language code
gettext: po/modules/log/log_uk.po: log_uk 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.