A meteor with a transmitter lands on earth, and you have to learn the alien language, starting with only numbers, then science, then more and more abstract and even personal ideas. Basically the part in Project Hail Mary where Grace tries to learn Rocky's language stretched out to about 30 hours and nearly 1000 messages. The basic game play loop is you have to deduce what a gradually introduced set of symbols mean through context, and then use your translations to answer questions the meteor asks you, to demonstrate understanding of a message, so you can progress to the next message. There are hundreds of words to define, and while some of them do mean specific recognizable things, many of them don't map cleanly onto english words, and the game never tells you what any the words are supposed to mean, officially.
I just spent a week powering through it and it's one of the best puzzle games I've played.