The description of the druid’s Wild Shape feature says, in part (PHB, p. 67):
You can’t cast spells, and your ability to speak or take any action that requires hands is limited to the capabilities of your beast form.
And the Mimicry trait of a raven says:
The raven can mimic simple sounds it has heard, such as a person whispering, a baby crying, or an animal chittering. A creature that hears the sounds can tell they are imitations with a successful DC 10 Wisdom (Insight) check.
As a druid PC, I’ve heard all the simple sounds that make up a language that I can speak. So, by RAW, can I speak all the languages my character knows while wildshaped in raven form? After all, I do keep my character’s mental abilities when I am in Wild Shape; am I able to mimic sounds well enough to speak?
If so: As slowly or weird-sounding as it may be, would it be clear enough for other people to understand?