How did Ishwak Singh deliver the most dialogues in Berlin without speaking?

In a recent interview with us, Ishwak Singh told us about his modern school in Delhi, where he spent 4 years. He is also an architect. People used to tell him that becoming an architect is not within his reach. Ishwak is very talented. He is multi-talented, he believed that if he wanted to do something, he would do it. During the interview interaction, he was asked about his school friends, his reply was that he is still connected with his school friends and he also made some friends who were not very close friends in school, but have become special now. The question was how did Ishwak deliver dialogues in the film Berlin without speaking anything, Ishwak’s answer was that there were a lot of dialogues which he delivered in sign language. It took him months to learn this sign language but he learned it very well.