It is Islamic doctrine that the Koran is not truly translatable, and some (perhaps all) schools hold it blasphemous to even try to translate it. By contrast it is a glory of Christianity that the New Testament is translatable, with the unsurpassed parables of Jesus helping define things. ("Who is my neighbor?" he asked, and Jesus told the story of the good Samaritan.) When God sent angels to us, he didn't demand that the men and women who heard him first take a crash course in Arabic--He spoke to them in their own languages.