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?
I don’t know, in the same book “There sure were a lot of babies in there, Carl” which hits pretty hard on how much murder Carl is doing and on how Donut really isn’t a human being.