I think the African Grey, in particular, have been shown to actually talk - in the sense of using language to convey meaning, rather than just mimicking. Tolkien's use of talking ravens is almost realistic, much more than the way many of the other animals behave in the books.
Google Alex the African Grey and have some fun. Alex is dead now but he was a brilliant talker. Upwards of a 900 word vocabulary. Einstein at the Knoxville Zoo, also an African Grey is a wonderful talker as well
My black-cap conure has a a vocabulary of 35 words and is easily understood. And crows at least are very intelligent. Now ravens think they are better than crows so one would hope they are also more intelligent with (in Tolkien-s world) language capabilities.