[Kalimac]

Hmmm...all of this makes a lot of sense, hadn't thought of it before. Ungoliant was definitely much more, how to put this, un-animal-like than Shelob - she specifically wanted jewels and fine things which Melko(r) promised to her, which implies a much more human-like mind at work than in Shelob's case: "Little she knew or cared of Rings, or towers" or anything except her appetites. But one thing I just remembered is that Tolkien mentions Shelob's descendants spreading to the fastnesses of Mirkwood, and those spiders could obviously speak some sort of language, though they don't give the impression of being any more interested than Shelob in the finer things. It's mostly food for them, too. Maybe the influence of Ungoliant was being slowly diluted when it came to things besides the basic instincts.

So the odds are that she understood language at least, given her mother and her offspring. But as for speaking it - I still get the impression that whatever power of speech she had may have gone by the point in the story that we see her, possibly on the use-it-or-lose-it principle; whom would she have spoken with, after all? And if she'd really wanted to terrify the hobbits into not resisting (especially Sam, at the end) a spoken word or two would certainly have helped.

As for Gollum; well, maybe it was a one-sided conversation? He sees her, squeals in terror, starts backing off and promising things to her, she pauses and listens in interest, he takes her not eating him as a sign that she's considering it. It's definitely a shadow of the scene where he's promising to feed Ungoliant "with both hands." Can't believe Shelob would have pity on anything, though, however wretched; it just isn't in her.

The only thing about that is, Gollum being in the state that he is, he would seem like the last person capable of producing decent food (he can't even feed himself properly). Maybe she just figured that he wasn't worth eating by himself and who knew, maybe he'd actually come through on his promise.