One interesting thing about the Foreigner books is how much of the Atevi culture is a slightly warped version of Japanese culture. Back in the mid-1500s to the early 1600s, the Japanese kept the Portugese and Dutch traders separate from the mainland on an island in Nagasaki after the disrupting influence of foreign ideas, trade, and religion led to internal conflict between factions. Later problems from even that attenuated contact led Japanese leaders to break off all relations with the outside, which is what Bren’s position as an ambassador is supposed to prevent from happening with the Atevi.
The humans and Europeans were similarly surprised at how quickly the ideas and technology given to the Atevi and Japanese respectively were adapted, changed, and in some cases improved by a group with no previous exposure to them. Only a few years after firearms were introduced, the Japanese had figured out a superior matchlock mechanism to the original Portuguese one. Industrial progress in Japan was frighteningly fast after being re-opened to foreign trade in the 1800s.
The Atevi and Japanese languages are opaque to outsiders, complicated and difficult to learn perfectly, and require convolutions that almost require you to be born into the society to get right. With the Atevi it’s the linguistic changes to reflect number, placement, speakers present, etc. With old Japanese, and to some extent with modern Japanese, truly polite language involves a different vocabulary, different grammar and verb formations, and must be adjusted to reflect the relative status of the individuals speaking, as well as taking into account the social situation and group membership. Simplified modern Japanese 敬語 keigo and 尊敬語 sonkeigo in today’s far less stratified post-War society is complicated enough that even native speakers have to practice it and receive some instruction in it to use it properly, though arguably the instruction is necessary because the honorifics aren’t used as often as they used to be.
The Atevi man’chi are analogous to Japanese networks of loyalty and influence. Similar to the mentions of Atevi period dramas that even Bren finds difficult to follow, Japanese jidaigeki are enduringly popular, and abominably complicated. A thorough knowledge of history is recommended and loyal viewership is mandatory to make any sense out of them. Plot twists often hinge on some previously hidden loyalty coming into conflict with the character’s official duties or role.
There are tons of other parallels that you’d pick up if you know about Japanese history and society. Obvious differences are that the Atevi are larger and stronger than humans. The humans, while technologically superior, have nowhere else to go, and their only currency is their technological knowledge. Therefore they have to do a delicate balancing act between letting out enough information to remain useful while not giving away everything or providing things that would destabilize the current leader.
This is not to knock Cherryh’s world-building, but to show that even with obvious influences and parallels to real life Japan, she has done some interesting things with those ideas as a jumping-off point. She takes a similar set of conditions, tweaks them a bit, and then plays with the consequences of those changes, while at the same time introducing some elements original to her and narrating it all in a style that is unquestionably unique.