One of the things that struck me about this movie is that whilst the focus is on learning to communicate with the aliens, that's not all that's going on.
Look at the scenes where Louise talks to Colonel Weber about what she's doing. She and he look at the world in different ways - they are also alien to one another, and she is using examples and stories - even made up ones like the "Kangaroo" story - to bridge a gap in understanding with him and his superiors, exactly like she's having to do with Humans and the Heptapods.
And on a larger scale, the different nations with Heptapod ships in them all have different philosophies and ways of doing things, different ways of understanding the situation. And they also have to overcome those gulfs and communicate with one another to arrive at the solution.
So the movie is about communication not just with the heptapods, but on at least three different levels. The message seems to be that we are ALL aliens to one another, and the key to overcoming those divides is learning to communicate so that we can bridge the gaps in understanding between us.
