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 mikutter 's PO files:

gettext: plugin/achievement/po/ja_KS/achievement.po: ja_KS not a language code
gettext: plugin/activity/po/ja_KS/activity.po: ja_KS not a language code
gettext: plugin/activity_gtk/po/ja_KS/activity_gtk.po: gtk not a language code
gettext: plugin/activity_setting/po/ja_KS/activity_setting.po: ja_KS not a language code
gettext: plugin/bugreport/po/ja_KS/bugreport.po: ja_KS not a language code
gettext: plugin/change_account/po/ja_KS/change_account.po: ja_KS not a language code
gettext: plugin/command/po/ja_KS/command.po: ja_KS not a language code
gettext: plugin/console/po/ja_KS/console.po: ja_KS not a language code
gettext: plugin/extract/po/ja_KS/extract.po: ja_KS not a language code
gettext: plugin/extract_gtk/po/ja_KS/extract_gtk.po: gtk not a language code
gettext: plugin/gtk3/po/ja_KS/gtk.po: gtk not a language code
gettext: plugin/notify/po/ja_KS/notify.po: ja_KS not a language code
gettext: plugin/openimg/po/ja_KS/openimg.po: ja_KS not a language code
gettext: plugin/proxy/po/ja_KS/proxy.po: ja_KS not a language code
gettext: plugin/search/po/ja_KS/search.po: ja_KS not a language code
gettext: plugin/set_input/po/ja_KS/set_input.po: ja_KS not a language code
gettext: plugin/set_view/po/ja_KS/set_view.po: ja_KS not a language code
gettext: plugin/settings/po/ja_KS/settings.po: ja_KS not a language code
gettext: plugin/shortcutkey/po/ja_KS/shortcutkey.po: ja_KS not a language code
gettext: plugin/smartthread/po/ja_KS/smartthread.po: ja_KS not a language code
gettext: plugin/sound/po/ja_KS/sound.po: ja_KS 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.