After discussion on the 9 Feb 2012 committers' call, the decision was made to provide fault codes for Fedora errors that are independent of the Java exception specifics. These are for use in the Web APIs as a way of distinguishing otherwise similar error conditions on the client side. See:
for more info.
Chris Wilper did some work a long time ago to begin internationalization for Fedora's exception hierarchy. It looks like (because this work hinged on providing codes for each exception underneath ServerException) it could be swiftly reused for this purpose, and we'd even get machinery for i18n for free!