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 zoneminder 's PO files:

gettext: web/api/lib/Cake/Test/test_app/Locale/cache_test_po/LC_MESSAGES/default.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/cache_test_po/LC_MESSAGES/dom1.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/cache_test_po/LC_MESSAGES/dom2.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/nld/LC_MESSAGES/default.po: nld not a language code
gettext: web/api/lib/Cake/Test/test_app/Locale/po/LC_MESSAGES/default.po: po not a language code
gettext: web/api/lib/Cake/Test/test_app/Locale/po/LC_MESSAGES/test_plugin.po: po not a language code
gettext: web/api/lib/Cake/Test/test_app/Locale/po/LC_MONETARY/default.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_0_po/LC_MESSAGES/core.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_0_po/LC_MESSAGES/default.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_10_po/LC_MESSAGES/core.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_10_po/LC_MESSAGES/default.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_11_po/LC_MESSAGES/core.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_11_po/LC_MESSAGES/default.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_12_po/LC_MESSAGES/core.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_12_po/LC_MESSAGES/default.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_13_po/LC_MESSAGES/core.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_13_po/LC_MESSAGES/default.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_14_po/LC_MESSAGES/core.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_14_po/LC_MESSAGES/default.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_15_po/LC_MESSAGES/core.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_15_po/LC_MESSAGES/default.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_1_po/LC_MESSAGES/core.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_1_po/LC_MESSAGES/default.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_2_po/LC_MESSAGES/core.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_2_po/LC_MESSAGES/default.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_3_po/LC_MESSAGES/core.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_3_po/LC_MESSAGES/default.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_4_po/LC_MESSAGES/core.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_4_po/LC_MESSAGES/default.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_5_po/LC_MESSAGES/core.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_5_po/LC_MESSAGES/default.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_6_po/LC_MESSAGES/core.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_6_po/LC_MESSAGES/default.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_7_po/LC_MESSAGES/core.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_7_po/LC_MESSAGES/default.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_8_po/LC_MESSAGES/core.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_8_po/LC_MESSAGES/default.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_9_po/LC_MESSAGES/core.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Locale/rule_9_po/LC_MESSAGES/default.po: can't guess language
gettext: web/api/lib/Cake/Test/test_app/Plugin/TestPlugin/Locale/po/LC_MESSAGES/test_plugin.po: po not a language code
gettext: web/api/lib/Cake/Test/test_app/Plugin/TestPlugin/Locale/po/LC_MONETARY/test_plugin.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.