Lars has written a fantastic analysis of Deleuze’s analysis of Foucault. This sheds a good deal of light on Deleuze’s understanding of language and his engagement with Hjelmslev.
Deleuze is insistent in his book on Foucault: despite appearances, despite the fact his recently deceased friend placed emphasis on discourse, he was a thinker of what Deleuze calls visibilities (and we should not be too quick to look for a definition of this word).
The elegant, but complex argument of Deleuze’s Foucault shows us how saying and seeing, ‘discursive practices and forms of self’evidence’ are divided – how the articulable and the visible, the forms of expression and the forms of content never quite coincide even as they combine to make possible particular behaviours, mentalities or sets of ideas that belong to particular historical formations (strata).
And not only that. Deleuze wants, too, to show how Foucault thinks their interrelationship as it draws upon a ‘non-relating relation’ such as Blanchot formulated it (albeit in a different context), which will require a unique ontology made up of folds and foldings, of the single plane of the outside that lends itself to particular interiorisations, but periodically shakes them out like a tablecloth, only to allow new crumplings, mutations by way of which new behaviours, mentalities and sets of ideas are distributed.
You can read the rest here.