NC as this is massively outing. My nationality is not English, but I have lived in this country since I was a baby. My features, skin etc obviously give me away, but hearing me you would think I was an average Brit. I speak my native language BADLY and my family take the piss out of my accent, etc. Anyway...
The reason I think it may be slightly rooted in racism is that DH and SIL are white and I am not. All his previous girlfriends were white and then he married me.
DH and I have been together for 6 years, married 2. In that time SIL has had a few kids and is always talking about babies/adoption. Mostly harmless but she will slip into territory I am uncomfortable with. We'll be having a perfectly normal conversation and out of nowhere she will ask me things like:
"Sunny, why is child abuse so prolific in your country?"
"Sunny, why don't you lot like having children?" [note: DH and I are childfree and my home country has a low birth rate].
"Sunny, why are there so many children up for adoption in your country?"
I bat these away with vague answers, but recently she has got it in her head that she's going to adopt a child from my home country. She is sending me links, articles and videos to adoption sites. I'm really not interested but don't feel like I can rock the boat. She has no plans to learn the language DH is conversational and keeps saying that I can talk with the kid to make it feel at home! 
Never mind that we live on opposite ends of the country, she works a NMW job and her house is already too small for her current family. I think that she has got to be winding me up, except this has been going on for years, who can be bothered to keep a 'joke' like this going for so long?