They've had years to hire Arabic and other language speaking people to monitor for these things, but I think the real reason the accounts don't get frozen ASAP is that various intelligence and law enforcement agencies around the world need the accounts kept open to track activities. Otherwise, it means the management at Twitter has always been criminally negligent. And yes, I saw the FBI agent's quote within the plaintiff complaint. Methinks he perhaps doth protest too much, to keep their strategic investigations mum.