Invader [Foreigner 2] by C. J. Cherryh
This is the second book in the Foreigner series. It's a sequel to Foreigner.
The premises of the series are: About 200 years ago, a lost starship left a crewed space station orbiting an Earth-like planet. The planet was already inhabited by an intelligent basically humanoid atevi race. A crisis forced the space station crew to go down to the planet. Humans and atevi think and assume so differently that misunderstanding led to war. Humans lost and were isolated on one island, Mospheira. All contact between the two species is now through a single human diplomat / translator. Humans maintain a bargaining position with their more advanced technology. The unexpected return of human starship has complicated matters more.
Bren is the human diplomat. With this book he must deal with the human starship Phoenix which reappeared at the end of the last book. This has raised major suspicions and planning among the atevi. It has also accentuated the factional lines within both human and atevi circles. Conservative atevi become more anxious about the modernization by the atevis led by Tabini and the humans he makes deals with.
Human factions become clear with the activities of Deanna Hanks, a secondary human diplomat. When Bren is away from the atevi it's her job to act as diplomat. But she has gotten the job through political connections, not skill. When Bren returns to the atevi, she doesn't go home and the human government is silent. By ignorance and/or factional agendas she increases tensions between atevi groups and in human-atevi relations.
While Bren struggles with high-stakes politics, he also faces troubled relationships with his family and a girlfriend, the progressive effects of emulating an atevi mind, and issues of identity.
This book gives us a deeper view of atevi society, politics and language than Foreigner.