Answer:
The narrator and his father agreed that a "common language" is not always necessary for communication.
Explanation:
The question above is related to a novel entitled "Dragonwings," written by Laurence Yep. The story centers on the character of "Moon Shadow Lee" who grew up in China and became reunited with his father in the U.S.A.
The situation above is a conversation between Moon Shadow Lee (narrator) and his father. His father taught him that even if they can't understand or speak with the demons, somehow, there is a common language that helps people communicate with them. He further added that it goes the same way with explaining about diagrams or numbers, no matter the person's accent, people can understand him (simply because it is "numbers"). This is the "common language" he was talking about.
So, this explains the answer.
