Re: why in arabic
Peace All
As far as I understand the Qur'an is the Word of God. It was revealed in Arabic and that is the way it should be recited. If it was revealed in another language and Allah (SWT) is All-Powerful then we would be required to recite it in the language it was revealed.
Du'a is better to be done in ones own language, but with du'a there are traditions and those traditions stem from the legacy of the Sunnah which is in Arabic. That is the reason why Khutba is done in the language of the listeners and parts of it are retained in the original Arabic tongue due to traditions that we are bound by.
Islam is the acknowledgement that all languages are from Allah (SWT) and that the Last Testament was revealed in Arabic and many parts of our rituals and customs are in accordance with our Arabic traditions.