I experience this a lot! I mean I spend all my time outside of Sfi with people whose native language is Swedish, pretty much, and we talk Swedish quite a bit. Which mostly means they talk Swedish and I go "ja..." a lot and nod. I understand! I know words! But they do hide so. (I'm being a little hard on myself, I manage to speak more than that; but one's ability to talk does lag frustratingly behind one's ability to understand.)