When a process instance is started the tasks are all assigned the language "en-UK" by default. Language is a parameter in some of the task API calls but must always be set to "en-UK" in order for the queries to work. Apparently the language setting is done in the work item handlers. If the system is going to support localization the language setting must be functional. It's not clear if this is supposed to be a current feature or is part of a planned future release. This jira was created in response to this forum post:
https://community.jboss.org/message/744858#744858