I actually know the guy (online, if it’s who I think he is) and he is a decent-enough guy. I haven’t read the article yet (blocked at work) but I know the circumstances at the time. Your argument fails on the grounds that saying that ANYONE teaching their children a foreign language at home might be considered child abuse. Seriously, would you tell a Sri Lankan couple they couldn’t use Tamil at home (in the US) as that’s “child abuse”? Kid soak up language, and they easily pick up the dominant language around them the moment they start school or pre-school. As someone with a foreign-speaking wife (and son) I am quite familiar with how kids with foreign-born parents actually end up as perfect speakers of the local language.

Now, obviously Klingon is of limited use in the ‘real world’ outside of fun and academic study (yes, as a constructed language it has genuine academic applications). However, in this case because the language is actually quite limited in vocabulary (less so in grammar), the child quite rapidly outstripped the ability to express everyday things in it – it’s all very well being able to order someone to fire photon torpedoes, but if you can’t even ask for a glass of (cow’s) (milk) then the average three-year-old will start to use another language – which is what happened here. So it was an interesting experiment, nothing more. [‘Official’ Klingon was created by one man, Marc Okrand, and relies on his very occasional addition of vocabulary and grammar, so misses much ‘everyday’ lanaguage.]

And by the way, plenty of studies have shown that multi-lingual kids have much better language abilities when older, so it’s unlikely to have actually harmed him.