labingi

My number one is The Goblin Emperor by Katherine Addison, alias of Sarah Monette. I loved it so much I didn't want it to end. I desperately want more of Maia and his world. Reviews which express very well how I feel: "remarkably compelling and fascinating", "mostly eschews plot-heavy histrionics in favor of warmth, psychological depth, and hope", and "compelling attractiveness of Maia’s character" as a fundamentally decent person, as well as the author's detailed worldbuilding.
Monette says she's writing a sequel featuring a minor character. I have hope of more Maia-ness despite that.

Becky Chambers' The Long Way to a Small, Angry Planet. Alien and human characters, very engaging and likeable.
Its sequel, A Closed and Common Orbit, focuses on two minor characters from the first book and is very, very different: an intense and fascinating exploration of AIs.
Both are optimistic and satisfying, but I'd say the second one is more powerful and other-culture.
The third book, set elsewhere in the same universe, didn't grab me as much and is not as different from US culture as you probably want. I read a novella as well, set in a different universe, but it was depressing which the two recced books certainly aren't.

Ascending by Meg Pechenick, an immersive novel about a linguist on a ship of aliens. It's slow starting (but never boring because linguist) but once she's on the ship you get the alien culture.
The sequel, Bright Shards, is also good but lacks the exploration of culture in the first. I'll certainly read the third. There is also some romance in this one.