Dear 100 Hour Board,
In Star Wars books with Chewbacca is it the case that: (1) his dialogue is written in English and it's explained at the beginning that anything he says is in his growling language, (2) onomatopoeia such as "rrwwww, arrrghh" are written, followed by expository language clearly written for the reader's benefit in response "Okay, Chewie, we'll go to the Hoth system for DQ Blizzards, (3) he doesn't get any dialogue, just mentions of things he does, (4) something else.
This doesn't exactly answer your question but I just read an article explaining that the issue with writing dialogue for Chewie was one of the reasons why Disney retconned the expanded universe. Writers thought it was hard to write dialogue for him so they killed him off but then Disney had the opportunity to bring him back in the newest movies (because nostalgia is a powerful money-making device) and they didn't want to explain that he was absent because a moon was dropped on him. It definitely would have been weird to hear about that for the first time in the theaters since I definitely did not read any of the EU.
I've read tons of Star Wars books, but it's been awhile. If I remember correctly, Han is usually the only one who really understands Chewbacca, so any other viewpoint character either relies on his explanations or doesn't really understand. Leia eventually gets a rudimentary knowledge of the language, and at one point she meets a Wookie with a speech impediment that makes him easier to understand for humans. I distinctly remember those conversations being written out in English because Leia knew what was going on.
With hundreds of novels and nearly that many authors, I don't think it was terribly consistent. Probably everything you mentioned happens off and on. But from what I remember, probably the most common are simple statements such as "Chewbacca growled in his language."
Dear Petey Boy,
I can't speak for the books, but in the comics it is squarely situation #2, which I like because I feel like it mirrors the movies.
Wookiee dialogue without any context is disastrous; if you want evidence, just watch the opening 10-15 minutes of the Star Wars Holiday Special (but you should really just take my word for it on this one, because that special is an abomination and is one of the most painful things I have ever watched).