Lol, for us French natives, that last bubble by the little brother would mean he already knows it's his brother. X) Why? Because otherwise he would have said "Je suis content que tu sois contente." This is how gender plays a part in our grammar. =/
@Shizomist This is probably the case here. But using foreign languages people are unfamiliar with could mislead other foreign people about one's language. It's like non-English people trying to explain it to other non-English speakers.