well, you could also consider that when Lefi learned to speak, the "olde English" was the norm, and that up to know, she did not have any reason to learn the new English, as she is not really interacting with people, and as her "olde English" is enough for her rare interaction with people. Being a non native English speaker I did not have much trouble to read/understand her, compared to other translation where they rely heavily on slangs and streets expression that leaves me completely clueless.