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 debian-policy 's PO files:

source does not specify a priority
gettext: locales/ja/LC_MESSAGES/ch-relationships.po:1148: duplicate message definition...
locales/ja/LC_MESSAGES/ch-relationships.po:64: ...this is the location of the first definition
msgfmt: found 1 fatal error
gettext: locales/ja/LC_MESSAGES/upgrading-checklist.po:4132: duplicate message definition...
locales/ja/LC_MESSAGES/upgrading-checklist.po:86: ...this is the location of the first definition
msgfmt: found 1 fatal error
gettext: locales/zh_CN/LC_MESSAGES/upgrading-checklist.po:4256: duplicate message definition...
locales/zh_CN/LC_MESSAGES/upgrading-checklist.po:94: ...this is the location of the first definition
msgfmt: found 1 fatal error
      

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.