Yeah, this one got me, too.
At the time of the book, Hindustani was used to mean both Hindi and Urdu (Hindustani had two forms, Modern Standard Hindi and Modern Standard Urdu). So... yeah, I guess it both is and isn't a language, given that its two composite parts are definitely languages.
As far as I remember, my parents never stopped me reading anything, probably because they were both voracious readers when they were children and it was their escape so knew that I was most likely the same. They also knew that if they told me I couldn't read something, that would make me want to read it so much more than if they hadn't said anything.
Other side to this though was that, instead of giving me The Talk, my mum just gave me a book because, and I quote (from about two weeks ago) "we knew you would read about it anyway so it might as well have been from a book we'd picked".
This reminded me - I had a high sleeper bed with a little reading light clipped to the frame. My parents had to resort to putting a timer on the socket the light was plugged into to stop me from reading past my bedtime, figuring that if I tried to unplug said timer, I'd wake them as I climbed down. WRONG. I got very good at creeping down that ladder and avoiding the creaky floorboard.
Back in my babysitting days, the mum I used to babysit for (who is now an actual friend of mine which is amazing) was an English teacher, so their living room was just full of books - so many that they were double-stacked. I think it was just a coincidence that some of the more trashy ones were at the back rather than the front, but that was as much about them being the kind of thing you'd take on holiday and not mind if the salt water ruined the pages as they were ones that they didn't want their girls reading.
What is it with 15 year olds and Wideacre? My friend from school had the series and it just got passed around our friendship group. And then when I went to uni, I found out that virtually every other girl I met who had been to an all-girl's school had the same thing at exactly the same age: someone (usually someone with slightly conservative parents) had the trilogy and the books moved through their group like some sort of black market for smut.