This one may be a bit of a stretch, but hear me out. Alucard's sprites may suggest he actually spoke to Trevor telepathically! Classically, Dracula himself was telepathic, so Alucard could have inherited the ability from his father. Now that the arguable canonical theory has been established, let's look at the game itself.
- Exhibit A: When Trevor meets Alucard in CV3, whenever Alucard talks he leans toward Trevor ever so slightly and gestures with his hand (it's kind of lewd, if you ask me). We never see Alucard's mouth move. Since he's a mystical figure, he could be a telepath.
- Exhibit B: When Trevor meets Grant in CV3, whenever Grant talks he visibly opens his mouth, unlike Alucard. Grant is a normal human and not a mystical figure, so he cannot be a telepath.
- Exhibit C: When Trevor meets Sypha in CV3, whenever Sypha talks she just nods her head. We never see her mouth move, but unlike Alucard, she has a hood covering her face. Since Sypha is a mystical figure, she could either be a telepath or she speaks with her obscured mouth.
- Exhibit D: Alucard gestures far more deliberately than any other character while talking. I argue he is either trying to emphasize his thoughts with gestures so Trevor can better understand the voice in his head, or the gesturing and posturing is actually Alucard physically projecting his thoughts into Trevor.
I think Grant proves that in CV3, if they wanted a character to talk vocally, that character's sprite would portray it. Sypha's face is obscured because she's a witch and also because the devs wanted to keep her gender vague. But I think Grant, hands down, backs up the argument that Alucard was a telepath.