This is my attempt to understand this beautifully opaque remark. 

Wittgenstein: if a lion could speak, we could not understand him. (PI, p.223)

The remark seems to generate a paradox. Why is it paradoxical? If a creature could speak, then we could understand him. Presumably, it matters little in what language the speaker speaks, because it is possible to translate the language into our own (Lionese to English). And a language is learnable. So, if a lion could could speak, we could understand him. But this Wittgenstein denies. Why?

The claimed paradox rests on a misunderstanding. Not every sentence in a language has a clear use.  Nor every word in a sentence. But does this mean that we could understand the lion if we are clear about his communicative intention? No. For the lion could only specify this to us by means of further words! They could even be translated into our own language. But this is no guarantee that they could be understood. In other words, it looks as if the meaning of words is not told by words alone, nor by the speaker’s intention.

Suppose a zoo lion says to you in English, “Life is unfair. I was born in captivity, and I shall die in captivity”.  I assume that we are clear on what the lion is saying here. There are two linguistic formations. Each formation is a sentence, constructed according to the rules of syntax. Further, we can identify the individual constituents of each sentence, and specify their meaning. But something is missing. Wittgenstein’s lion, it seems to me,  is not about what is said, but that it is said. We distinguish between what the lion is saying, and that he is saying it.

How on earth are we supposed to take the lion’s speech? Suppose you and I are conversing, and we overhear a conversation behind us. I ask you, “Who is speaking?” You reply, “Oh, the lion is”. The situation jars. Why? Prior experience means we don’t expect it? Is the problem experiential? Might future experience reveal a world populated with conversing lions? No. Experience cannot inform me of this. Rather, isn’t it that our instinct tells us that lions could not have any conceivable share in our world? A dog hopes his master is at the door. But can it hope that his master is at the door tomorrow? Instinctively not. If a dog could speak, we could not understand him.

Well enough. But what does “lions could not have any conceivable share in our world” mean exactly?