The interpreters at my airline in China all went to an aviation university and have to do 4 week ground school for the 737. Exactly the same course as any pilots doing a 737 type rating in China. They do have aviation knowledge although obviously not the same as a pilot, however some of them think they are the same level as the pilots. In my company the translators actually wear the same uniform as the first officer including the 3 gold bars!!! Causes a bit of resentment sometimes, especially from the cabin crew as the cabin crew get paid more, but the interpreters get the same crew meal as pilots etc. Also our interpreters only fly about 40 hours a month; the rest of the time is spent doing office based work. All in all it works out, and as said earlier they don’t talk on the radio, just translate if the crew can’t understand each other.