80 percent of language is non verbal. That means the nephew will need to learn a new non spoken language. Non spoken language is all the eye rolls, looks, body movements, and facial expressions that give us clues about how our family is feeling. So you will need to spend time with the boy, and be willing to explain moods and other social clues to him. the first year will be the hardest. Just think that the boy is from another country and has to learn about living in his new country.
Best wishes
Best wishes