We all know that Arabic is the Language of the Qur'an and that Allah revealed the Qur'an in Arabic and that Arabic is the "Language of the Heavens". "Is it obligatory to learn the Arabic Language? If some one does not know Arabic then what will he do when the angels come to his grave for questioning him after his death and on the Day of Judgement when he will meet Almighty Allah face to face" How will people communicate with the angels and Almighty Allah in the Hereafter?Please justify your answer by the light of Al-Qur'an and the Sunnah if possible.

Praise be to Allah, the Lord of the Worlds; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
Belief in those matters which are from the unseen such as the language in which the angels will question in graves and the language used at the Day of Resurrections, these matters should be believed as stated in the Qur'an and Sunnah. But the belief in them is a distinguished quality of good Muslims. Allah Says (interpretation of meaning): {Alif-Lâm-Mîm. [These letters are one of the miracles of the Qur'ân and none but Allâh (Alone) knows their meanings]. This is the Book (the Qur'ân), whereof there is no doubt, a guidance to those who are Al-Muttaqûn [the pious and righteous persons who fear Allâh much (abstain from all kinds of sins and evil deeds which He has forbidden) and love Allâh much (perform all kinds of good deeds which He has ordained)]. Who believe in the Ghaib}[2:1-3].
There is no evidence in the Qur'an or Sunnah that identifies the language of communication in the after life. As a general rule, discussing the matters of the unseen or trying to know their reality without having any evidence of the Qur'an and Sunnah is not permissible.
All organs of human beings will witness against him if he commits something wrong Allah Says (interpretation of meaning): {This Day, We shall seal up their mouths, and their hands will speak to Us, and their legs will bear witness to what they used to earn. (It is said that one's left thigh will be the first to bear the witness).}[36:65].
It is very possible that Allah might make a common language for all His creatures in the Day of Judgement, or He may address everyone in the language which is convenient to him. It is also possible that Allah might make the angels who question in grave able to understand the language of every person.
A Muslim should not engage himself in such matters, he should aim only at performing good acts which help him to be steadfast in this very moment. This could be achieved by implementing the rules of Shariah and avoiding all prohibitions. The key for being steadfast in these critical moments is firm faith in Allah and implementation of Shariah Allah Says (interpretation of meaning): {Allâh will keep firm those who believe, with the word that stands firm in this world (i.e. they will keep on worshipping Allâh Alone and none else), and in the Hereafter}[14:27].
Allah knows best.