Foreigner [Foreigner 1] by C. J. Cherryh
This is the first book in the Foreigner group of books by the author.
The essential premises of the story are historical events that occurred about 200 years before the setting of the book. The starship Phoenix had left Earth to colonize a known area of the galaxy, but exited hyperspace in an unknown part of the galaxy. Having no idea where they were, they couldn’t go home. They found an Earth-like planet, built and crewed a space station orbiting it, and Phoenix left to explore further. The planet was already inhabited by an intelligent basically humanoid race. A crisis forced the space station crew to go down to the planet. The natives, atevi, had different customs, beliefs, assumptions and mental approaches than humans. Communication was very difficult. Misunderstanding led to war - humans lost. The humans were isolated from the atevi by being restricted to one island, Mospheira. All contact between the two species is now through a single human diplomat / translator. Humans have more advanced technology than the atevi. The ability to slowly dole this out gives humans the bargaining power to remain on the planet safely.
The book centers around the current human diplomat, Bren Cameron. He not only has to do the tricky translation between such different languages and assumptions, he must juggle a political situation where both humans and atevi have factions that are xenophobic and/or have conflicting agendas.
The atevi society has a system which allows killing approved by the independent Assassin's Guild. An unauthorized assassination attempt against Bren brings the factional power plays to a higher level. Bren must navigate through the perilous situation that could result in catastrophe. Part of the conflict centers around reactions to human technology and modernization in the traditionalistic atevi society. The future of humans is in question.
Through Bren's knowledge of and interaction with the atevi, we learn about an alien culture. We get an unusual variant on human-alien stories - here, humans are a restricted minority on a world of bigger, stronger and (at least in some ways) brighter aliens. By having the story center on such a diplomat, we are faced with the possibility that relations with aliens may be a long, confusing and dangerous process - not something that has a few bumps before a solution makes the problems vanish forever.
The book (and the series) is a bit more like Sherlock-Holmes-as-interspecies-diplomat than an action or exploring-new-worlds-travelogue book. Not that Bren is so much like Holmes, but it's more cerebral untying of knots than most SF. This works for some readers, but not all.