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 bzflag 's PO files:

gettext: data/l10n/bzflag_da.po:1273: duplicate message definition...
data/l10n/bzflag_da.po:400: ...this is the location of the first definition
msgfmt: found 1 fatal error
gettext: data/l10n/bzflag_en_US_l33t.po: can't guess language
gettext: data/l10n/bzflag_en_US_redneck.po: can't guess language
gettext: data/l10n/bzflag_ru.po:2065: 'msgid' and 'msgstr' entries do not both end with '\n'
msgfmt: found 1 fatal error
gettext: data/l10n/bzflag_xx.po: xx 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.