Yeah, I can't see Cass being multilingual. She learned English very late (after she became Batgirl!) and previously read body language instead. She actually had to be taught English by the previous Batgirl, Barbara Gordon. Babs has always been Cass's main mentor instead of Bruce, though he's the one who ended up adopting her (which seems to be back in canon after New 52 erased it, the latest issue of Birds of Prey has her appear out of nowhere, earning a "you're your father's daughter" comment - definitely sounds like it's referring to Batman).