accessing draft mailing leads to 500 error - localization?

After upgrading to 4.7.13, a group stopped being able to load a draft email.

The nginx error log reported:

"PHP message: PHP Fatal error: Class name must be a valid object or a string in /var/www/powerbase/sites/all/modules/civicrm/CRM/Utils/SQL.php on line 46"

The error is in the CRM_Utils_SQL::mergeSubquery - which is being called with an empty $entity variable.

That's empty due to the CRM_Core_DAO::addSelectWhereClause() which iterates over the results of: $this->buildOptions('entity_table', 'get');

That function returns a table named "civicrm_group_en_US" (since this site is multi-lingual).

That value is then passed to CRM_Core_DAO_AllCoreTables::getBriefName(CRM_Core_DAO_AllCoreTables::getClassForTable($table)); which doesn't return anything.

This problem seems to have originated with CRM-19448.