My Great Old One warlock just made third level, and I chose Pact of the Chain. I chose an imp as a familiar initially (recasting find familiar would allow me to change to an ordinary familiar or any of the other special familiars, as well as retrieving the familiar spirit if the physical form is killed), with the intention that the imp would usually remain shapeshifted into the form of a raven — to avoid awkward questions about alignment, for the most part.
That said, the imp is one of the familiars that can actually speak, both the common tongue and Infernal. Since ravens have been taught to talk (like parrots) for centuries, it wouldn't be instantly obvious the raven is more than it seems, at least to someone who doesn't know find familiar themselves. The question is, can the imp still speak when shapeshifted to raven form?
I'm not asking to be able to speak through the familiar — that's a separate invocation on my wish list for a few levels later. I don't need the imp to speak to me, of course; we have telepathy for that. But can the imp speak its own words when in the form of a raven?
Best Answer
Yes, it can
The imp's stat block is clear in how the shapechanger trait mechanically works. It states in the PHB (p. 277 with my emphasis):
It's always an imp, it just resembles other forms
Part of the Imp's statistics are it's languages, and those remain the same.
It's also important to note that it isn't actually a raven, it's an imp in a form that resembles a raven.