It's a secret he's been holding to his chest, closely, though it's no surprise that the people who knew his family back when remember. Stiles, of course, knows about his fluency in Spanish though none of the others for years.
It's only when Stiles and John invite him on their trip to Poland to visit their extended families that Derek decides to let them know that Polish is one of the languages he always spoke and understood.
Teen Wolf, Derek (implied Derek/Stiles)
It's a secret he's been holding to his chest, closely, though it's no surprise that the people who knew his family back when remember. Stiles, of course, knows about his fluency in Spanish though none of the others for years.
It's only when Stiles and John invite him on their trip to Poland to visit their extended families that Derek decides to let them know that Polish is one of the languages he always spoke and understood.