On various making-of specials and DVD/BR extras you can find footage from the set of the original Star Wars movies where Chewbacca speaks English. I'm not sure but it may be just Peter Mayhew in the costume speaking
Obviously these lines were dubbed over in the final movie and Wookies speak Shyriiwook in the official universe, but something I've never been able to find a definitive answer to is whether or not the original plan was for Chewbacca to speak English.
On the one hand it makes sense that it would just be lines spoken by the actor in the costume so that the other actors like Harrison Ford could react to it, similar to how David Prowse spoke lines from the Darth Vader costume that were overdubbed by James Earl Jones later. On the other hand we know that in the original movie there were labels with English writing on them that were digitally changed to the Aurebesh alphabet, and there's an anecdote circulating that David Prowse wasn't informed ahead of time that his voice was going to be replaced.
Is there a definitive answer out there as to whether or not it was always intended for Chewbacca to speak Shyriiwook or was it going to originally be English?