Installation was a breeze, with two small exceptions. Fist, "ISO language codes" can be either two or three letters. It seems the one we were supposed to enter is "se" - which is neither of them, but the two-letter country code. (For Sweden, not for Swedish...) No biggie. The other thing is it took me 20 minutes to realize I was actually already done with the installation - on the Components > Joom!Fish > Translation screen you have to select something in the "content elements" dropdown or it looks as though there is nothing you can translate. Pretty obvious when you know it although I would have used "all" as default rather than "none".
All in all - this really works. I'm happy.