The language-bound objection applies to Christianity too: the Bible was written in Hebrew and Greek, and most Christians can’t read it. And doesn’t “careful preservation shows careful copying” undercut the site’s own use of manuscript preservation as evidence?

Both points are fair and should be conceded. The difference that can be defended is that Christianity does not claim the Bible’s literary form is its proof; it claims historical events are, and events can be assessed in translation. On preservation, the Reliability of Scripture case uses it to answer the charge of corruption, not to prove inspiration, and the same standard applies to the Qur’an: excellent preservation, which Christians can freely grant, shows what Muslims say it shows about transmission, not about origin. That symmetry is exactly right.