Wahrheit ist unteilbar, kann sich also selbst nicht erkennen; wer sie erkennen will, muß Lüge sein.
Truth is indivisible, hence it cannot recognize itself; anyone who wants to recognize it has to be a lie. [Kaiser/Wilkins]
The truth is indivisible and is therefore incapable of recognizing itself; whatever claims to recognize it must therefore be a lie. [Hofmann]
Hofmann marks this once cancelled, but Kaiser/Wilkins do not.
The Hofmann translation, by saying "incapable," deprives truth of the ability to recognize itself, whereas Kaiser/Wilkins could be read to mean that the truth is circumstantially prevented from exercising a power of recognition that might exert otherwise.
Truth could only recognize itself if it were divisible, which would make it possible for one part to encounter another part and, by dint of some kind of comparison, to a model or image, or measurement according to some other criteria, most likely the criteria by which the truth was divided up, recognize it as another piece of the truth.
This is a little like the point Bergson makes in Creative Evolution, that, owing to our limitations, humans can only manage to take it a bit of nature at a time, and so humanity has to put together its picture of nature a piece at a time, knowing that, since all of nature is interconnected and basically one, we have to try to bring all our theories into a single consistency, and keep revising the overall model, which itself is too large for any one person to see, every time a new theory appears.
What is more radical here is the idea that truth can only be known from falsehood. Is the reverse true? The difference between a lie and the truth is intention; I can say something unwittingly true while I think I'm lying and, morally speaking, I will still be a liar. I can know with greater assurance, greater truth, when I'm lying, because a lie must be accompanied by an intention to lie. If I say something untrue without meaning to, that's not a lie, but a mistake.
I don't need to know the truth in order to lie, because the lie is tailored to the situation, not measured against knowledge. But in order to know the truth, I have to know the difference between truth and untruth, although it's a stretch to call all untruth "lies." Besides, Kafka isn't talking about how a person knows a difference, but how truth knows itself. It can't, only the lie can know the truth and recognize it as object whose shadow it is.
This to me hearkens back to the aphorisms in which good cannot know itself as good, in which only the evil can know good, such as Number Twenty-Seven and Number Twenty-Eight.