Many people have praised Hellspark. I will skip the plot squib and say what I love about this book: the joy. All the characters are having so much fun learning and understanding and realizing and connecting and figuring it out. The reader is absolutely in on the game, as well; there's a running stream of little details about people's cultures that you can pick up and run with.
(Trivial example: early on, the protagonist introduces her computer (and starship) to a new friend: "Lord Lynn Margaret", meet "Tinling Alfvaen". Elsewhere, the ship is the Margaret Lord Lynn -- therefore, it must be that Alfvaen is a personal name, Tinling is a family name, and the protagonist is politely transforming her ship's name into Alfvaen's native idiom. And also that, at some point, "Lord" as an English-idiom title has become gender-neutral... All of this is completely unremarked in the narrative. You just go with it.)
Also: the puns. I don't mean the narrative is a groanfest; you just run into these little bits of translation that work out to be bilingual puns (in two fictional languages). Or bilingual puns between a fictional language and English body language. For posture, gesture, distance, and all such nonverbal communications are part of language; thus they can be spoken with an accent, translated poorly... and punned in. Delightfully.
It is not a perfect book. The points of view of the various cultures is never quite smooth, from the inside. The author needs to convey the unconscious assumptions of each character, but does it more by explicit description than by clean implication. The story is presented as a murder mystery, and less formally as a first-contact SF story (which is of course always a mystery plot). But the murderer is unmasked several chapters before the end, and the pacing of revelation of both mysteries is awkward. I never had the moment of "Of course, how could I have missed..." -- in either plot thread. I'm also unhappy with the guilty faction, the "Inheritors of God", who are shallow villains with no sympathy to them -- too easy to dismiss. Conveying their interior assumptions and viewpoint would have turned a delightful book into a brilliant one.
We do not complain of these matters, because we're having too much fun hanging around with the characters. I mean, the non-murdering ones.
Obligatory amused complaint: I have the first-edition Tor paperback in which the title of the book is misspelled on the front cover. The fact that this is possible -- and yet not noticeable to the reader until chapter 3 -- is one of the charms you will have to discover.