In a scene before her trial, Rebecca is seen in her chamber praying. She is at the side of her bed on her knees. Jewish people do not kneel when they pray (except on Yom Kippur.)
When Sir Brian de Bois-Guilbert signs the letter, the words are in modern English, yet the Normans even at that time would have spoken and written in Norman French. If they despised the Saxons as inferior, there is no way they would condescend to even learn their language.
At the very end as Rebecca leaves the castle, we see the sea in the background. But York is inland.