Visible crew/equipment: When Arthur is riding with his knights in the open field, there's a front shot of the cavalry line. When the camera lowers down to where we can see the legs of the horses, the trail of the camera stage is visible on the ground.
Visible crew/equipment: In the scene where king Arthur is on a horse walking across a frozen lake, you can see a huddle of camera equipment in the background. The next shot is from that spot.
Visible crew/equipment: In the last fight, when the first Saxons enter the door, there is a doorstop visible to keep the door open. (01:47:50)
Answer: I don't think it's supposed to be German. Probably Old Saxon. Could be something like "slahten fiand" - slaughter enemy.