Isn't a big part of Arrival that the aliens don't experience time the same way we do? Or something along those lines. When something that fundamental is different, that has to become a major hurdle in communication.

Whereas the aliens in Project Hail Mary are still fundamentally similar organisms. And you just have to come up with a common baseline to understand each other. Humans have been able to learn to translate between different languages for a long time now. It seemed no different than that to me. Especially when you add in machine assistance.

I would actually be quite curious though. If you put two people in a room, and each one only speaks one distinct language, and their only goal is to communicate with each other. How long before they can effectively communicate? Now it wouldn't be a perfect comparison because there is likely shared body language. It would still be interesting.