Walking in to a greeting like Callie's broad smile was something that Theo didn't think he could ever get used to, that strange pleasure at seeing someone so happy just to see him with no ulterior motive or guile. Languages had always been something that had come easily to Theo, a polyglot in the truest sense. He'd spoken to Blaise in Italian in the past, to Draco in French; when he was distressed or sometimes when he dissociated after a nightmare he had a tendency to slip into Russian. It might just have been the fact that he was a bored child and had nothing better to do, something about the way his mind worked or some hidden desire to escape expressed by travelling the world by tongue.
He was happy enough to speak in English with Callie though, his expression drawing down into curiosity and concern at what she said, because of course Theo's mind would suspect danger before anything else. "Of course. For you, I have hours." he promised, gingerly taking a seat in case she wanted him to follow her.