As for becoming accustomed to talking to one another in a language other than Arabic, which is the symbol of Islām and the language of the Qurān, so that this becomes a habit in the land, with ones family and household members, with ones friends, in the marketplace, when addressing government representatives or authority figures or when speaking to people of knowledge, undoubtedly this is makrooh (disliked), because it involves being like the non-Arabs, which is makrooh, as stated previously.
Hence when the early Muslims went to live in Syria and Egypt, where the people spoke Byzantine Greek, and in Iraaq and Khurasaan, where the people spoke Persian, and North Africa (al-Maghrib) where the people spoke Berber, they taught the people of those countries to speak Arabic, so that Arabic became the prevalent language in those lands, and! all the people, Muslim and kaafir alike, spoke Arabic. Such was also the case in Khurasaan in the past, then they became lax with regard to the language and got used to speaking Farsee until it became prevalent and Arabic was forgotten by most of them. Undoubtedly this is disliked.
The best way is to become accustomed to speaking Arabic so that the young people will learn it in their homes and schools, so that the symbol of Islām and its people will prevail. This will make it easier for the people of Islām to understand the Qurān and Sunnah, and the words of the Salaf, unlike a person who gets used to speaking one language, then wants to learn another, and finds it difficult.
Know that being used to using a language has a clear and strong effect on ones thinking, behaviour and religious commitment. It also has an effect on making one resemble the early generations of this Ummah, the Companions and the Taabieen. Being like them improves ones thinking, ! religious commitment and behaviour.
Moreover, the Arabic language itself is part of Islām, and knowing Arabic is an obligatory duty. If it is a duty to understand the Qurān and Sunnah, and they cannot be understood without knowing Arabic, then the means that is needed to fulfil the duty is also obligatory.
There are things which are obligatory on all individuals (fard ayn), and others which are obligatory on the community or Ummah (fard kifaayah, i.e., if some people fulfill them the rest are relieved of the obligation).
This is the meaning of the report narrated by Aboo Bakr Ibn Abee Shaybah who said: Eesa Ibn Yoonus told us from Thawr from Umar Ibn Yazeed that Umar wrote to Aboo Moosa al-Asharee radiallaahu anhu and said: Learn the Sunnah and learn Arabic; learn the Qurān in Arabic for it is Arabic.
According to another hadeeth narrated from Umar radiyallaahu anhu, he said: Learn Arabic for it is part of your Religion, and learn how the estate of the deceased should be divided (faraaid) for these are part of your Religion.
This command of Umar, to learn Arabic and the Shareeah combines the things that are needed, for Religion involves understanding words and actions. Understanding Arabic is the way to understand the words of Islām, and understanding the Sunnah is the way to understand the actions of Islām.
See also: [Learning Arabic in an obligation (Fard) on EVERY Muslim]