The following contains spoilers for the film Arrival. You really don't want this movie spoiled for you.
Arrival is the rare smart science fiction movie where the battle is waged with words rather than guns. The film's climax is brilliant for many different reasons, but one of them is a mystery that the film leaves open. What exactly was it that Louise Banks said to General Shang which causes him to stand down his impending attack on the alien visitors? Now, thanks to the screenwriter, we know the answer.
Different nations treat the alien visitors with different degrees of suspicion in Arrival. While Amy Adams' character spends all of her time and effort trying to not only translate the words of the alien language, but verify their meaning, others are not nearly so patient. Eventually, the Chinese make the decision to attack the aliens, at the same time that Adams' Lousie Banks begins to understand how the alien language truly works. This leads to a frantic phone call from Banks to China's General Shang where she repeats back to him the last words of Shang's dead wife. However, as the line is in Chinese, and not subtitled, we have no idea what is said. Screenwriter Eric Heisserer was present at the Alamo Drafthouse's Fantastic Fest when he revealed what the line was. According to Thrillist, who was there, the line translates to...
The decision was made by director Denis Villeneuve to leave the line a mystery. Apparently, Eric Heisserer was less interested about leaving it ambiguous, which is part of why he has so readily now revealed the truth. It does seem a little odd as a place to insert mystery, specifically because if you happen to speak Chinese, there was no mystery. Only those without that language were left in the dark.
In the end, the line is really unimportant. The scene is not about what the line is, but rather about how Louise Banks learns the line, by understanding that her knowledge of the alien language gives her an understanding of time that allows her to learn the line for the first time by experiencing a time in which she already knows it. We could look at it as the line being ignored so the audience would focus on the more important aspect of what's going on or we could look at it as a curious decision to hide a mostly meaningless piece of information.
Now that the mystery is solved we can all go back to focusing on what's important, which is that Arrival is an amazing movie and for some reason which passes understanding Amy Adams was not nominated for an Academy Award. Regardless, the film is up for several more at the Oscars which will be broadcast February 28.