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 mailman 's PO files:

gettext: messages/es/LC_MESSAGES/mailman.po:11286: `msgid' and `msgstr' entries do not both begin with '\n'
messages/es/LC_MESSAGES/mailman.po:11439: `msgid' and `msgstr' entries do not both end with '\n'
messages/es/LC_MESSAGES/mailman.po:11560: `msgid' and `msgstr' entries do not both end with '\n'
msgfmt: found 4 fatal errors
gettext: messages/fr/LC_MESSAGES/mailman.po:7138: `msgid' and `msgstr' entries do not both end with '\n'
msgfmt: found 1 fatal error
gettext: messages/hr/LC_MESSAGES/mailman.po:1709: `msgid' and `msgstr' entries do not both end with '\n'
messages/hr/LC_MESSAGES/mailman.po:1758: `msgid' and `msgstr' entries do not both end with '\n'
messages/hr/LC_MESSAGES/mailman.po:4537: `msgid' and `msgstr' entries do not both end with '\n'
msgfmt: found 3 fatal errors
gettext: messages/ia/LC_MESSAGES/mailman.po:70: `msgid' and `msgstr' entries do not both end with '\n'
messages/ia/LC_MESSAGES/mailman.po:1485: `msgid' and `msgstr' entries do not both end with '\n'
messages/ia/LC_MESSAGES/mailman.po:1838: `msgid' and `msgstr' entries do not both end with '\n'
messages/ia/LC_MESSAGES/mailman.po:2503: `msgid' and `msgstr' entries do not both end with '\n'
messages/ia/LC_MESSAGES/mailman.po:3123: `msgid' and `msgstr' entries do not both end with '\n'
messages/ia/LC_MESSAGES/mailman.po:3127: `msgid' and `msgstr' entries do not both end with '\n'
messages/ia/LC_MESSAGES/mailman.po:3220: `msgid' and `msgstr' entries do not both end with '\n'
messages/ia/LC_MESSAGES/mailman.po:3515: `msgid' and `msgstr' entries do not both end with '\n'
messages/ia/LC_MESSAGES/mailman.po:10789: `msgid' and `msgstr' entries do not both end with '\n'
msgfmt: found 9 fatal errors
gettext: messages/ja/LC_MESSAGES/mailman.po:2117: `msgid' and `msgstr' entries do not both end with '\n'
messages/ja/LC_MESSAGES/mailman.po:5377: `msgid' and `msgstr' entries do not both end with '\n'
messages/ja/LC_MESSAGES/mailman.po:5419: `msgid' and `msgstr' entries do not both end with '\n'
messages/ja/LC_MESSAGES/mailman.po:6209: `msgid' and `msgstr' entries do not both end with '\n'
messages/ja/LC_MESSAGES/mailman.po:8398: `msgid' and `msgstr' entries do not both end with '\n'
msgfmt: found 5 fatal errors
gettext: messages/nl/LC_MESSAGES/mailman.po:2210: `msgid' and `msgstr' entries do not both end with '\n'
messages/nl/LC_MESSAGES/mailman.po:3679: `msgid' and `msgstr' entries do not both end with '\n'
messages/nl/LC_MESSAGES/mailman.po:5862: `msgid' and `msgstr' entries do not both end with '\n'
msgfmt: found 3 fatal errors
gettext: messages/pl/LC_MESSAGES/mailman.po:1338: `msgid' and `msgstr' entries do not both end with '\n'
messages/pl/LC_MESSAGES/mailman.po:1568: `msgid' and `msgstr' entries do not both end with '\n'
msgfmt: found 2 fatal errors
      

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.