What is the ruling on calling a Muslim a Jew?

It is not permissible to call a Muslim a Jew. There is no harm in speaking Tamazight or other languages when needed. However, if there is no need, the default is to speak Arabic, because it is the language of the Qur’an and the emblem of Islam. Furthermore, habituating a language affects one's intellect, character, and religion. Knowledge of the Arabic language is an obligatory duty for understanding the Book and the Sunnah.