$string['privacy:metadata:pcast_episodes:subtitle'] = '?';
$string['privacy:metadata:pcast_episodes:keywords'] = '?';
$string['privacy:metadata:core_rating'] = '?';

Run phpunit tests to see the errors:

vendor/bin/phpunit tool_dataprivacy_metadata_registry_testcase admin/tool/dataprivacy/tests/metadata_registry_test.php