Anil Biltoo, the London-based linguistics specialist who taught actor Michael Fassbender the Proto-Indo-European language that David speaks in the film, said that during his major moment with the engineer, the delighted android exclaimed, "This guy is here because he does not want to die."
Biltoo told The Guardian, "It's a very common German phrase which means 'the guy is here because he has not been killed yet.' It's a bit like if I said to you, 'I'm going to kill him,' and then didn't.'"
Fassbender was able to convey the meaning of this statement without using any English words. He simply acted it out with hand gestures and by showing the engineer objects that he had with him in the room. This demonstrates that David can communicate ideas through simple actions.
In addition to being an expert on ancient languages, Biltoo is also familiar with modern technologies. He explained that Fassbender used these skills to communicate with David. He said, "He [Fassbender] showed the engineer things around his neck. Then he put his hand up to his head and made a gesture as if to brush something away. I think the engineer took this as a sign that he should still build the robot."
So David can communicate through actions and expressions, just like any other human being.
Anil Biltoo of the SOAS Language Centre in London, who functioned as Prometheus' Linguist Teacher, has disclosed what David stated in an interview with The Bioscopist (via Ropes of Silicon): "This man is here because he does not want to die." He feels you can give him a new lease on life. Anil translated most of the conversations that David had with people outside of the spaceship.
When asked if he could communicate with other aliens, Prometheus replied in the affirmative but added that it was dangerous because they might decide not to help him.
Prometheus also said that there were three types of aliens: those who wanted to harm humans, those who wanted to help them and those who were indifferent to their fate. He went on to say that although he hoped for the last category, it was difficult to judge from his conversation with them if they were actually going to be friendly or not.
When asked how long he had been in space, Prometheus replied that he did not know but believed it to be several years based on where he had come from and what had happened to him. He added that he had tried to leave Earth many times but always ended up back again.
Prometheus also mentioned that there was one thing that could kill him: "She" (whoever she was). He said that when he was first brought on board the ship, it was because someone wanted to study him.
Dr. Anil Biltoo, the film's official translator and linguistics expert, says David did what he was requested, interpreting his remarks as follows: "This man is here because he does not want to die."
Biltoo also notes that when David told the engineer he had a wife and child, this must have made sense to him since it is customary for Indians to believe that everyone has a family back home.
Finally, Biltoo points out that David doesn't go against his religion by performing an operation like this one. He only does what people all over the world do every day: eat food, drink water, use the toilet.
So in conclusion, he says, "David just wants to live a normal life."
Now, what did the engineer say back? We will never know because the camera stopped recording. But we can assume something along these lines: "OK, come with me," he said, and then he walked off into the darkness with the boy following him.