Is talking and joking in a language understood by everyone present except for one person considered a private counsel (najwa), and is it permissible for the person affected to leave the gathering, or should they remain patient out of consideration for kinship?

If the speakers speak Arabic and are able to converse in it, then their action contravenes the Law of Allah and the teachings of His Noble Messenger, who urges harmony and affection. It also considers the Arabic language among the rituals of Islam, and is likewise a transgression against proper etiquette with their companions and kin.