Never Call a Muslim a Jew
6-3-2012 | IslamWeb
Question:
What is the Sharee‘ah ruling on a person who calls a Muslim a Jew? The reason why I am asking such a question is because I live in Libya and speak the Amazigh language and consequently the Arab people there call us Jews.
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad 
is His slave and Messenger.
It is not allowed for a Muslim to call his fellow Muslim a Jew or any other non-Muslim names. The Prophet explained that if a person calls anyone a disbeliever while he is not so, this will surely rebound upon him with a grave sin. [Al-Bukhari and Muslim] This is a sufficient deterrent and punishment for whoever calls his fellow Muslim such names. There is nothing wrong with a Muslim speaking the Amazigh language or any other non- Arabic language as long as there is a need that requires that. An example of such a need may be that this is the native tongue of the society in which a person lives, irrespective of whether this language is the person's mother tongue or not.
However, if there is no need to speak a foreign language, like in the case of a person who lives in a non-Arab country within an Arab society and can speak Arabic, it is undesirable to speak in a foreign language. The Arabic tongue is the slogan of Islam and its followers; furthermore, languages are one of the most important characteristics of nations according to which they are distinguished from one another.
Consequently, some scholars have said that it is undesirable for those who can speak Arabic to speak in a foreign language or even to combine them without a need.
When he heard some people speak the Persian language, Muhammad ibn Sa‘d ibn Abi Waqqaas 
indicated that this was an imitation of the Magians. Ash-Shaafi‘i said that it is undesirable for a person who speaks Arabic well to speak in any other language as Arabic is the language in which the Quran was revealed. He also said that a person should learn Arabic if he is able to do so.
Shaykh Al-Islam Ibn Taymiyyah said that it is disliked to speak in a language other than Arabic, to the extent that this becomes an outstanding feature of a family or a town because this is an imitation of the non-Muslims, which is unfavorable under the Sharee'ah (Islamic law).
Ibn Taymiyyah further pointed out that when Muslims conquered countries that did not speak Arabic, they were such an influence on them that they taught them to speak Arabic. As time has passed, people have become accustomed to speaking foreign languages to the extent that they have deserted Arabic altogether.
Shaykh Al-Islam went on to say that Arabic affects the mind, morals and religion of the person positively and helps him imitate the Companions and the successors of the Prophet, sallallaahu ‘alayhi wa sallam, which necessarily improves his mind, faith and morals.
According to the aforementioned citations, it is reprehensible to speak in a non-Arabic language unnecessarily, but if it is necessary, there is nothing wrong with doing so. It is also impermissible to call a Muslim a Jew or anything else, just because he speaks Amazigh or any other language.
Allaah Knows best.