I'd say this is harmless. Actually, probably brain expansive for the kid. Really, it's not different from friends of mine whose parents only spoke Dutch German to them in the home - although they live in an English-speaking society. The kids picked up English just fine through interactions outside the home, and are bilingual. Makes me jealous sometimes, really. lol. So, what's the big deal if this kid is bilingual with English and Klingon?