Consider this argument against divine ineffability: Let p be the conjunction of all fundamental truths intrinsically about God (I'm thinking here of something like the Jon Jacobs account of ineffability, but the point should work on other similar accounts). Stipulate that the sentence "It divines" (a feature-placing sentence or zero-place predicate, like in "It rains") expresses p. It divines. It seems I have just said the conjunction of all fundamental truths intrinsically about God. Hence God is not ineffable.
But this argument cannot be sound, since God is in fact ineffable--divine ineffability is, for instance, part of the creed of the Fourth Lateran Council. So what goes wrong with the argument?
First, one might have technical worries about infinite conjunctions or arbitrary linguistic stipulations. I'll put those to one side, though they are worth thinking about.
More deeply, one might worry whether there are any fundamental truths intrinsically about God. Truths are true propositions. Perhaps the fundamental reality of God not only cannot be expressed in language, but cannot even be given propositional form. I am not sure about this, though it is a promising response to the argument. But, plausibly, propositions are divine thoughts. And God surely does express his fundamental reality in his thought (indeed, this is central to Augustine's Trinitarianism).
I want to try out a different response to the argument: question the last step in the argument, the inference "Hence God is not ineffable." This response allows that we can stipulate and assert a sentence that means the conjunction of all fundamental truths intrinsically about God, but denies that this is a problem for ineffability. Ineffability isn't a denial of the possibility of asserting a sentence whose semantic content is such-and-such truths about the divine nature. Rather, it is the denial of the possibility of linguistically communicating these truths. For me to linguistically communicate a truth to you it is required that my sentence give rise to your thinking that truth. But the truth expressed by "It divines" isn't a truth you can think. On this understanding, divine ineffability is an immediate consequence of divine incomprehensibility, and rather than being a doctrine about semantics, it's a doctrine about communication.
If this is right, then stipulation allows the semantics of our language to outrun communication and thought. You can think some deep philosophical truth that I don't know, and I can stipulate that "It xyzzes" means that truth, and I can sincerely assert "It xyzzes." But I don't thereby think that truth. I can, of course, think the second order thought that "It xyzzes" is true, but to do that is not the same as to think that it xyzzes. Similarly, I can think that "It divines" is true, but that's a thought about a piece of stipulated language rather than a thought about God. Indeed, it divines, but I don't understand the sentence "It divines" as I can't grasp the proposition it expresses.
Sometimes people are accused of a certain kind of insincerity like this: "You're just saying the words but don't really understand." This is a different kind of insincerity than when people are lying. A person who is "just saying the words" may believe that the sentence composed of the words is really true, and if so, then she isn't lying. (Corollary: One can say something one doesn't believe and yet not be a liar, as long as one believes that what one is saying is true.) The reason that there may be insincerity in "just saying the words" is that normally one implicates that one believes (and hence has a minimal understanding of) the content of what one says. But that's an implicature that can be canceled to avoid even this kind of insincerity: "I don't exactly know what 'God loves you' means, but I believe that it is true. God loves you." And when people are talking of a topic neither is close to being an expert on, the implicature of understanding one's words may be contextually canceled.