14:4 We sent not an apostle except (to teach) in the language of his (own) people, in order to make (things) clear to them. Now God leaves straying those whom He pleases and guides whom He pleases: and He is Exalted in power, full of Wisdom.
30:22 (Y. Ali) And among His Signs is the creation of the heavens and the earth, and the variations in your languages and your colours: verily in that are Signs for those who know.
41:44 (Y. Ali) Had We sent this as a Qur'an (in the language) other than Arabic, they would have said: "Why are not its verses explained in detail? What! (a Book) not in Arabic and (a Messenger an Arab?" Say: "It is a Guide and a Healing to those who believe; and for those who believe not, there is a deafness in their ears, and it is blindness in their (eyes): They are (as it were) being called from a place far distant!"
Only Apostle should know the language of the people who are supposed to guided and he is required to deliver message. Mandatory is belief ( Iman) and not language of the Book. Language itself is either Ayat / sign of Allah hence any language is acceptable to read Quran which after reading it with any believer can make its morals. After all Quran has verses which as in:
39:23 (Asad) God bestows from on high  the best of all teachings in the shape of a divine writ fully consistent within itself, repeating each statement [of the truth] in manifold forms  [a divine writ] whereat shiver the skins of all who of their Sustainer stand in awe: [but] in the end their skins and their hearts do soften at the remembrance of [the grace of] God. ( i.e Quran explains itself, if you believe in its message).
Quran has ayats for communication ( verses) and ayats for natural communication to understand and adjust life. Hence it is not necessary to know Arabic but to use reason for reading and exploration of the nature. God will create humanity and will not close door for humanity, as all the humans are blessed with eyes, ears and intelligence without exception.