I just started Dungeon Crawler Carl. In it he fights a Spanish speaking boss. The Spanish is not translated (so far) and if you can read it, it really changes the mood and impact of the entire scene.
Are there any other books that hide significant plot points behind the use of foreign language?
This is done with a fictional language in the first Nier game. You spend the whole time slaughtering hordes of enemies, but then new game+ gives them subtitles and makes you do it all again with context. It’s grim.