I do believe that Shelob does have both the consciousness and the language abilities to qualify. Remember, Gollum has a deal with her to deliver the Hobbits, which suggests they can speak to each other. That's the main evidence from LOTR.
But elsewhere in Tolkien's writings there is more evidence. Shelob, it turns out, is a daughter of Ungoliant, a corrupted Maia who ages ago took the form of a giant spider. Ungoliant bred with similar spiders already living in Arda, and Shelob was one product. Shelob's offspring form a large colony of giant spiders living in Mirkwood. These are the spiders that Bilbo encounters in The Hobbit. Since they possess the power of language, and Ungoliant must have, it makes sense that Shelob should, even if we don't actually see her speak.
Leprechaun, I think Ents belong with men, elves, etc, rather than with talking animals. By the way, the wild men are Woses.