I know that places where they used to, like Australia, no longer do that. I don't believe the U.S. has any regulations on that. I confess I don't know the details for Germany, but Lufthansa Technik has actually grown into a global maintenance group and I don't believe that Lufthansa is actually required to utilize them. But I confess I don't know the details on that. I'd say the norm throughout the world is no restrictions on where maintenance has to be done.
On May 2nd, 2016. See this statement in context.