We know that Raven can shapeshift and replicate anyone she sees. Is that limited to outer appearance? I mean will the vocal chords be replicated as well? Can she mimic someone without hearing them talk by simply shapeshifting to be like them?
It seems possible.
When she first meets Charles in X-Men: First Class (clip on YouTube), she pretends to be his mother and apparently mimics her voice. It’s implied that the impression comes from a photo on the wall. It’s unlikely that she’s heard his mother’s voice, as it’s the middle of the night and she’d be asleep.
Obviously, we don’t know if she sounds anything like Charles’s mother, but it’s a different voice to her own, and he doesn’t call her out for sounding different. So I think it’s possible that she can do it, but I don’t know a better example than this.