the second part about is Quran being in Arabic only for Arab and why it is in Arabic
The judgment concerning the people of the Book is the same as that of the polytheists concerning this matter. It is well known that there were both Arabs and non-Arabs among the polytheists, such as Turkish, Indians and others. So, all the polytheists are just like the Arab polytheists and all the people of the Book are just like the people of the Book amongst the Arabs. They are all included in the huge number, which is incomprehensible except by Allah, of the people who know the Arabic language.
It is not obligatory for every Muslim to know and understand every single verse of the Qur’an. But it is incumbent on him to know everything, which Allah commanded him to do and abandon everything, which Allah forbade him to commit, in whatever language he knows. That is quite possible for all nations and for all sorts of people from amongst the non-Arabs, such as the Persians, Turks, Indians, Berbers and other nationalities. Some of them know Arabic, while others came to know the obligations Allah enjoined on mankind through translation.As for these verses
Indeed, We have sent it down as an Arabic Qur’an that you might understand. (Yusuf, 12: 2)
And if We had made it a non-Arabic Qur’an, they would have said, “Why are its verses not explained in detail [in our language]? Is it a foreign [recitation] and an Arab [messenger]?” Say, “It is, for those who believe, a guidance and cure.” And those who do not believe – in their ears is deafness, and it is upon them blindness. Those are being called from a distant place. “‘ (Fussilat, 41:44)
Indeed, We have made it an Arabic Qur’an that you might understand. (Az-Zukhruf, 43:3).
These verses state how Allah conferred His blessings upon His servants by sending down the Qur’an in Arabic, for it is the most perfect language and the most powerful language as regards conveying meanings and figures of speech. Thus, it is considered a Divine blessing that the Qur’an was revealed in Arabic and not in any other language. In addition, it addressed the Arabs at first, therefore it was revealed in Arabic so that they could understand it. Those who learn their language will understand the Qur’an in the same way they do, while those who do not know their language, the Qur’an can be translated into their language at the hands of those who know their language. Moreover, it was not only a blessing bestowed upon the Arabs that the Qur’an was revealed in Arabic, for it also represented an obligation and a responsibility (that they have no excuse not to believe in it and that they should spread the religion all over the world.)
Quoted from Imam Ibn Taymiyyah ( died 1328) book in response to letter by the Greek church about Islam