TYPO3 Core

Context class : Tx_Workspaces_ExtDirect_ActionHandler

getRecipientList(…) calls (Tx_Workspaces_Service_Stages)->getResponsibleBeUser to get the default recipients from the stage configuration,
then sets lang info for each of those recipients using unserialized 'uc' field or 'lang' field.

Problem is that getResponsibleBeUser(…) only returns the following fields : 'username', 'uid', 'email', 'realName'.
So neither 'uc' nor 'lang' fields are available and lang information is NULL, resulting notification emails in default language.