When and if we receive communication from extra terrestrial life it will be simple. It will not be language. It will be signals that correspond to the make up of atoms. One signal would represent a proton, another signal will represent a neutron and a third will represent an electron. Three different signals could then convey the entire periodic table. There will be no two way communication due to the vast distance. It will simply be a signal that says “we are here, and hope you hear it.”
All advanced civilizations (and we are not advanced but merely in our scientific infancy) will understand atomic structure and that is what they would first convey to show they are sentient beings. They might even have more complex information in the same bursts that we can not detect due to our limited science at this time.
It must be put in perspective of the rate of advances in science. 20,000 years ago we lived in caves, had no written language nor history least it be oral. The man that lived in those caves is genetically almost identical to us today. Today we send men to the moon, fly airplanes at Mach III, have harnessed atomic energy for good and bad. We are but at the very beginning of scientific knowledge and advancement. Imagine a civilization that is 20 million years older than us, or for that matter 70 million as was the age of the dinosaurs.
I suspect space is filled with information from these civilizations if they exist and I think they do. At present we do not have the technology to pick up and decipher the message. I suspect they do not care if we can not as we would be rather uninteresting.
The simplist universal communication would be binary. On, off.
In my view, the Milky Way galaxy (let alone, the entire universe) is far too vast for me to assume that we, on this smallish mudball, circling a second rate star, in the hinterlands of an unremarkable collection of stars, are the one and only form of intelligent life there is.
There are two hundred BILLION stars in our home galaxy, and even more galaxies in the the observable universe. The staggeringly incomprehensible numbers involved, lean towards a universe teeming with life - advanced and otherwise.
At some point, we’re going to tap into a signal from one of them, though I highly doubt it will be anywhere in the radio spectrum, which is much too slow for interstellar communications.
We cannot understand the language of terrestrial bees, Apis mellifera.
We can’t hope to understand extraterrestrial Aliens.
They came, but since they looked like dogs, nobody paid any attention