The Status of the Arabic Language in Islām
An excellent explanation of the importance of learning al-ʿArabīc and an analysis of studying languages other than it.
The best way is to become accustomed to speaking al-ʿArabīc so that the young people will learn it in their homes and schools, so that the symbol of Islām and its people will prevail.
Shaykh al-Islām Ibn Taymīyyah
As for becoming accustomed to talking to one another in a language other than al-ʿArabīc, which is the symbol of Islām and the language of the Qurʾān, so that this becomes a habit in the land, with one’s family and household members, with one’s 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 ’ʿIrāq 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 al-ʿArabīc, so that al-ʿArabīc became the prevalent language in those lands, and all the people, Muslim and kāfir alike, spoke al-ʿArabīc. 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 al-ʿArabīc was forgotten by most of them. Undoubtedly this is disliked.
The best way is to become accustomed to speaking al-ʿArabīc 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 Qurʾān 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 one’s thinking, behaviour and religious commitment. It also has an effect on making one resemble the early generations of this Ummah, the Companions and the Tābi’īn. Being like them improves one’s thinking, religious commitment and behaviour.
Moreover, the al-ʿArabīc language itself is part of Islām, and knowing al-ʿArabīc is an obligatory duty. If it is a duty to understand the Qurʾān and Sunnah, and they cannot be understood without knowing al-ʿArabīc, 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 kifāyah, i.e., if some people fulfill them the rest are relieved of the obligation).
This is the meaning of the report narrated by Abū Bakr Ibn Abī Shaybah who said: ’Eesa Ibn Yūnus told us from Thawr from ʿUmar Ibn Yazīd that ʿUmar wrote to Abū Moosa al-Ashʿarī (raḍī Allāhu ʿʿʿanhu) and said: “Learn the Sunnah and learn al-ʿArabīc; learn the Qurʾānin al-ʿArabīc for it is al-ʿArabīc.”
According to another ḥadīth narrated from ʿUmar (raḍī Allāhu ʿʿʿanhu), he said: “Learn al-ʿArabīc for it is part of your Religion, and learn how the estate of the deceased should be divided (faraa‘id) for these are part of your Religion.”
This command of ʿUmar, to learn al-ʿArabīc and the Sharīʿah comibnes the things that are needed, for Religion involves understanding words and actions. Understanding al-ʿArabīc is the way to understand the words of Islām, and understanding the Sunnah is the way to understand the actions of Islām…” 
 Iqtidaa‘us-Siraatil-Mustaqeem (2/207)