Roughly described, a natural language interpretation system that provides commands to a back-end application in response to user input is modified to separate out user interaction functions into a user interaction subsystem. The user interaction subsystem can include an interaction block that is specific to each particular I/O agency, and which converts user input received from that agency into an agency-independent form for providing to the natural language interpretation system. The user interaction subsystem also can take results from the back-end application and clarification requests and other dialoguing from the natural language interpretation system, both in device-independent form, and convert them for forwarding to the particular I/O agency.