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 marble 's PO files:

gettext: poqm/ar/marble_qt.po: qt not a language code
gettext: poqm/be/marble_qt.po: qt not a language code
gettext: poqm/bg/marble_qt.po: qt not a language code
gettext: poqm/bs/marble_qt.po: qt not a language code
gettext: poqm/ca/marble_qt.po: qt not a language code
gettext: poqm/ca@valencia/marble_qt.po: qt not a language code
gettext: poqm/cs/marble_qt.po: qt not a language code
gettext: poqm/da/marble_qt.po: qt not a language code
gettext: poqm/de/marble_qt.po: qt not a language code
gettext: poqm/el/marble_qt.po: qt not a language code
gettext: poqm/en/marble_qt.po: qt not a language code
gettext: poqm/en_GB/marble_qt.po: qt not a language code
gettext: poqm/eo/marble_qt.po: qt not a language code
gettext: poqm/es/marble_qt.po: qt not a language code
gettext: poqm/et/marble_qt.po: qt not a language code
gettext: poqm/eu/marble_qt.po: qt not a language code
gettext: poqm/fi/marble_qt.po: qt not a language code
gettext: poqm/fr/marble_qt.po: qt not a language code
gettext: poqm/ga/marble_qt.po: qt not a language code
gettext: poqm/gl/marble_qt.po: qt not a language code
gettext: poqm/gu/marble_qt.po: qt not a language code
gettext: poqm/he/marble_qt.po: qt not a language code
gettext: poqm/hi/marble_qt.po: qt not a language code
gettext: poqm/hr/marble_qt.po: qt not a language code
gettext: poqm/hu/marble_qt.po: qt not a language code
gettext: poqm/id/marble_qt.po: qt not a language code
gettext: poqm/is/marble_qt.po: qt not a language code
gettext: poqm/it/marble_qt.po: qt not a language code
gettext: poqm/ja/marble_qt.po: qt not a language code
gettext: poqm/ka/marble_qt.po: qt not a language code
gettext: poqm/kk/marble_qt.po: qt not a language code
gettext: poqm/km/marble_qt.po: qt not a language code
gettext: poqm/ko/marble_qt.po: qt not a language code
gettext: poqm/lt/marble_qt.po: qt not a language code
gettext: poqm/lv/marble_qt.po: qt not a language code
gettext: poqm/ml/marble_qt.po: qt not a language code
gettext: poqm/mr/marble_qt.po: qt not a language code
gettext: poqm/nb/marble_qt.po: qt not a language code
gettext: poqm/nds/marble_qt.po: qt not a language code
gettext: poqm/nl/marble_qt.po: qt not a language code
gettext: poqm/nn/marble_qt.po: qt not a language code
gettext: poqm/oc/marble_qt.po: qt not a language code
gettext: poqm/pa/marble_qt.po: qt not a language code
gettext: poqm/pl/marble_qt.po: qt not a language code
gettext: poqm/pt/marble_qt.po: qt not a language code
gettext: poqm/pt_BR/marble_qt.po: qt not a language code
gettext: poqm/ro/marble_qt.po: qt not a language code
gettext: poqm/ru/marble_qt.po: qt not a language code
gettext: poqm/sa/marble_qt.po: qt not a language code
gettext: poqm/se/marble_qt.po: qt not a language code
gettext: poqm/si/marble_qt.po: qt not a language code
gettext: poqm/sk/marble_qt.po: qt not a language code
gettext: poqm/sl/marble_qt.po: qt not a language code
gettext: poqm/sv/marble_qt.po: qt not a language code
gettext: poqm/tr/marble_qt.po: qt not a language code
gettext: poqm/ug/marble_qt.po: qt not a language code
gettext: poqm/uk/marble_qt.po: qt not a language code
gettext: poqm/wa/marble_qt.po: qt not a language code
gettext: poqm/zh_CN/marble_qt.po: qt not a language code
gettext: poqm/zh_TW/marble_qt.po: qt 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.