Shadowspeak...Strange frowns, mulling it over. And, at least when he talks, he's lowered his voice to 'reasonable speaking level' (because really, whispering's equally as suspicious as shouting!)

"It makes sense why the Summer Fae couldn't translate it. The Winter Court seemed more likely to use shadows--and you found it in the Count's castle in the first place. The problem here is, I doubt we'll be run into any Winter Court fae friendly enough to provide a translation."

And the only person Strange knows who was remotely Winter Court during Portland (Childermass) spent most of his time around the Summer Court. Even if Childermass knew how to read shadowspeak, Strange doubted he remembered.