Hi..
I dont know arabic but i know even people are not arabic they do memorize the whole Quran letter by letter..so many people and all muslims knows some parts of the Quran in arabic memorizing..
So... it cant be changed, because there are so many people remember all letter till Muhammed saw's time.
I am turkish and there are turkish letters from may be 4-5 centuy i still have clue what they say..even we never keep it those old poem turkih and remeber allthe time and give meaning all the time and write lots of book about meaning all the time.. i still can understand general idea..
so If Allah says so clear.. They say: "Allah hath begotten a son": Glory be to Him, nay, to Him belongs all that is in the heavens and on earth: everything renders worship to Him. (The Qur’an El-Bagarah 116).. still people will understand..
honestly..if christians says bible's original language is almaniac .. there is no bible in its original language .. yet translate allthe time one language to others if they still claim that bible is the same and if you believe in that..than it is so easy to believe that The Quran is absolutey not been changed.