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 smplayer 's PO files:

gettext: setup/translations/po_files/albanian.po: can't guess language
gettext: setup/translations/po_files/amharic.po: can't guess language
gettext: setup/translations/po_files/arabic.po: can't guess language
gettext: setup/translations/po_files/basque.po: can't guess language
gettext: setup/translations/po_files/bulgarian.po: can't guess language
gettext: setup/translations/po_files/catalan.po: can't guess language
gettext: setup/translations/po_files/croatian.po: can't guess language
gettext: setup/translations/po_files/czech.po: can't guess language
gettext: setup/translations/po_files/danish.po: can't guess language
gettext: setup/translations/po_files/dutch.po: can't guess language
gettext: setup/translations/po_files/farsi.po: can't guess language
gettext: setup/translations/po_files/finnish.po: can't guess language
gettext: setup/translations/po_files/french.po: can't guess language
gettext: setup/translations/po_files/galician.po: can't guess language
gettext: setup/translations/po_files/german.po: can't guess language
gettext: setup/translations/po_files/greek.po: can't guess language
gettext: setup/translations/po_files/hebrew.po: can't guess language
gettext: setup/translations/po_files/hungarian.po: can't guess language
gettext: setup/translations/po_files/indonesian.po: can't guess language
gettext: setup/translations/po_files/italian.po: can't guess language
gettext: setup/translations/po_files/japanese.po: can't guess language
gettext: setup/translations/po_files/korean.po: can't guess language
gettext: setup/translations/po_files/malay.po: can't guess language
gettext: setup/translations/po_files/polish.po: can't guess language
gettext: setup/translations/po_files/portuguese.po: can't guess language
gettext: setup/translations/po_files/portuguesebrazil.po: can't guess language
gettext: setup/translations/po_files/romanian.po: can't guess language
gettext: setup/translations/po_files/russian.po: can't guess language
gettext: setup/translations/po_files/serbian.po: can't guess language
gettext: setup/translations/po_files/simpchinese.po: can't guess language
gettext: setup/translations/po_files/slovak.po: can't guess language
gettext: setup/translations/po_files/slovenian.po: can't guess language
gettext: setup/translations/po_files/spanish.po: can't guess language
gettext: setup/translations/po_files/thai.po: can't guess language
gettext: setup/translations/po_files/tradchinese.po: can't guess language
gettext: setup/translations/po_files/turkish.po: can't guess language
gettext: setup/translations/po_files/ukrainian.po: can't guess language
gettext: setup/translations/po_files/vietnamese.po: can't guess language
      

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.