Turns out that during filming, Peter Mayhew (the man in the Wookiee suit) just interacts in English.
The Shyriiwook chat only gets added in post-production. Mind blown!
Check this clip of Chewie rowing with Hans Solo in The Empire Strikes Back.
Wonderful bit of stuff from @jamieswb!! pic.twitter.com/oObW8Cll2f
— Peter Mayhew (@TheWookieeRoars) November 5, 2016
"Where the Hell have you been?"