My main problem here is that I don't know what to search for in Google, hopefully you guys can help out.
My story is set in a fictional country with a language based heavily on French. A girl from Britain was kidnapped and has just been located (she's now aged about twenty-five). I was thinking that she was probably taken at about age six or seven.
How much English, if any, would she remember, if she hasn't spoken English with anyone in almost twenty years?
I've googled combinations of "knowledge of language", "language acquisition", "language in a new country" and similar variations about accent. I have found some interesting information about the psychological impact of moving to a new country but no actual cases of knowledge of a mother tongue when re-introduced to it after a significant length of time.
Anything you can suggest would be greatly appreciated.
Edited to add
Thanks for the quick replies. The story of the children kidnapped by their father is very similar to what's going on in my story, I'm in the process of looking up the language retention search on Google, you're right, that is the sort of thing I'm looking for.
Thanks again for all the help.