As you say, they’d have to know Arabic. Many, though not all, Muslims consider translating the Koran or writing it in a script other than Arabic to be heretical.
In (very) partial defense of the Afghan response, Muslims view the Koran not just as a book, but as the Word of God, that it was uncreated and pre-existing for all time. Not particularly logical, but then religions, sort of by definition, aren’t often examplars of logic.
Thus “desecration” of the Koran is viewed much more severely by devout Muslims than similar treatment of the Bible is viewed by Christians or Jews. The view is much closer to “desecration” of a Host, which Catholics and Orthodox view as literally the Body of God. Accusations of the desecration of a Host was the usual trigger for pogroms during the middle ages and early modern times.
Yes, I think all religions consider the destruction of sacramental objects by non-believers one of the worst possible things.
That said, I’ve heard more than a few Afghan gov’t spokesmen and tribal elders say the insurgents aren’t real Muslims. Still, when they are said to be responsible for destruction of holy books or mosques, hell, even when they kill worhsippers, it doesn’t make much of a stir.