This is correct.
The Koran is just the start of Islamic jurisprudence, which is the core of this extremely legalistic religion. Reading the Koran is not a good way to understand Islam.
exactly. The Koran wouldn't make any sense by itself.
That is why Stephen Coughlin was and remains spot on correct to point out that we do not need to concern ourselves with what is the real Islam but only need to show what texts used by Muslims say, books which are on sale in Mosques or Muslim Bookstores all across the land, and which are for Muslim use to instruct what is proper doctrine.
The whole you need to know Arabic is nonsense, for per the OIC and with at least the concurrence of the highest scholarly authorities in Sunni Islam we do in fact find English as one of the official languages approved for such books, and they, if they are actually FOR Muslims and not for consumption by non-Muslims, apparently have to get some level of approval, to have that *bling* of scholarly blessing ... again, the Sunni world but the Shites etc will have their own respective authorities.
As you say, it’s legalistic ... so where many of Islam’s Useful Idiots don’t mind flying by the seat of their pants in excusing away Islam as the root of wars and terrorism (like how they glossed over the Fort Hood shooter’s apparently quite nuanced reasons for what he did) you can bet the terrorist frequently can’t play fast and loose too.