Adrian will be struggling not to fall into German, which will probably be easier via text than when voices get turned back on. He has a thing about people knowing his background. I'm headcanoning that he speaks Greek, Egyptian Arabic, French and Italian, because of his upbringing and the time he spent in the Middle East, plus being a freaking genius. He also probably can read Middle Egyptian and Coptic.

Mattie is all English all the time, and probably won't be much affected by the writing-only period either. Letter writing is clearly a lost art, here.