Speak English?

I don't think my child speaks English. He carries on LOOOONG conversations with toys, with the dog, with me, with the trash can, but I don't think its just baby jibberish, today it sounded more like German I think. We encourage him to talk, but apparently he enjoys speaking in other languages. He follows the layout of a conversation great- he yells at the dog in his own language, he asks me questions, and I even think he makes jokes because he laughs at himself (Yes, he does get that from me!). You know, I DO remember Josh doing this as a kid- he was about 5 or 6 when he'd do it though. He'd make up his own language and talk to us in his secret language and then look at us like we were dumb when we couldn't understand him. Maybe Mason is just being like Uncle JB, he's too smart for us!!