No no I've seen it (twice...second time was even better). I'm merely noting that it's, imo, likely that the aliens would have the ability to decipher our langua

No no I've seen it (twice...second time was even better). I'm merely noting that it's, imo, likely that the aliens would have the ability to decipher our language and communicate with us. Should they choose not to, then they must have a reason, which like you noted was the point of the story in Arrival.