I think the gubmint is telling us he can’t speak English, to shield us from his anti-American ideology and to prevent interviews which would outrage Americans. The other tactic the gubmint will use is to keep him in a hospital for a long time “due to health issues”. It’s all a load of crap.
Actually, it was the father who first suggested his kiddie had forgotten English. Or, in Jihadi-speak: “Don’t give the game away!”