Split-brain is a condition in which the right and left hemispheres of the brain are surgically separated. This is achieved by cutting-off the axons within the corpus callosum, the cerebral commissure that connects the two hemispheres. The hemispheres still may exhibit some connection through the brainstem, or other non-severed small commissures.
A split-brain person is able to speak intelligibly, because the motor control of both mouth and larynx are represented in both the hemispheres just like the fovea. Additionally, the function of the motor system is based on the collected inputs, not just a single neural input resulting in a single output. This may disconnect the topographic relationship established between the motor cortex and motor output. Although the corpus callosum is removed, other fiber tracts like the anterior commissure in the subcortical region helps the two hemispheres to communicate. This results in the coordinated movement of the mouth to produce a speech.
Both the hemispheres of the brain are responsible for the motor control by the action of mouth and larynx. Therefore the individual with a split brain will be able to be comprehensible.
The anterior commissure enables the communication between the two hemispheres other than the corpus callosum. Again, the input from collected neurons results in the motor actions. Thus the individual is comprehensible.