For everything that Katherine had learned about their family, Rebekah somehow doubted very much that she would have learned Old Norse. Why would she have bothered? The Originals had very much kept their origins shrouded in mystery so she wouldn't have had a reason to go poking about in that region of the world.
It was that, more than anything else that persuaded Rebekah that her first instincts had been incorrect. Pausing, she studied the girl, eyes still a bit wary. "...Tatia?"