"Gauru" may not be instinctive, but I would bet money that "Guru" — pronounced "guh-roo" or "guhr-oo", in accordance with the "ur" sounds of Urhan, Urshul and Urfarah, and not "goo-roo" like the far more common word — would have caused infinitely more confusion. And the "Garou" spelling wouldn't have fit the First Tongue, nor would a "Garu" variant.
The thing about the First Tongue, though, is that it's largely optional. For people who want to use it a lot, it's there — but the only things for which you really are expected to use First Tongue terms instead of English (or whatever) are the stuff for which English doesn't have convenient terms for anyway, like form names. The word "Uratha" is used throughout the core book, but not nearly as frequently as "werewolf" or "werewolves." The spirit world is called the Hisil, but usually as "the spirit world," "the Shadow Realm" or simply (as most werewolves would be inclined) "the Shadow."
The main issue, of course, is that we wanted all the specialized not-English terminology to come from one place: not a mix of French (Garou, metis), bastardized Latin (Glabro, Crinos, Hispo), less bastardized Latin (homid, lupus), obscure English (Galliard, Ragabash), Gaelic (brugh, fomori), and made-up stuff (Ahroun), to say nothing of the mishmash that was Fera terminology. In a few cases we bent the First Tongue rules to become their own things instead of following the original patterns, mostly when devising mnemonics (like the similarities of the auspice names to the previous auspices); tweaking our own rules to make it easier, not more difficult.
So I stand by the inclusion of the First Tongue over the loaded terminology of W:tA because it gives greater consistency. And as I say, there's maybe a dozen terms that you might use every session, and they're pretty easy to learn; read the book, make a sample character, and use makes it easy. There's more than a dozen terms for people who enjoy using them, of course, but most werewolves aren't going to be casually slipping First Tongue words into ordinary human-talk just to sound exotic
