We have had our 2 ~9mth old rescue cats for a week. They came from an old lady who had about 15 cats, according to the rescue centre, so they are not feral, but just not used to interacting with people and incredibly shy. We have been keeping them in "their" room until they stop hiding from us feel secure, and they are slowly working out what staff humans are for - boy is the bolder of the two, and has decided that he loves tickles, and has a lovely loud purr. Girl is very very shy still but will just about agree that tickles are tolerable and has started to play with toys when no-one is looking.
..but neither of them has said a word. Not a single Miaow. It's not (I don't think) that they don't have voices, as they don't do silent miaows - they just don't have anything to say 
Has anyone else come across this? I am used to noisy buggers quite vocal cats and I find it very strange. Do you think they will find something to say as they get more confident?