I heard one say a growly "Paiiiinnnn" the other day. I don't think they say things much, and if you have music/sound effects on high + voices low, you may miss noticing.
In terms of game lore...no idea. Seems like eventually it'd be hard for them to talk...rotting vocal chords and such.

Feral Ghouls are those who's minds have gone to another realm.
...They have the same regeneration ability that normal ghouls have.

Specifically, the neurotransmitters affected in a ghoul's mutation are those responsible for cardiac and respiratory function in a healthy human being. These transmitters are continually regenerated at a greatly accelerated rate after the mutation sets in, carrying sufficient oxygen to sustain the life of the subject while being insufficient to retain dermal elasticity and avoid the resulting necrosis (much like what happens during the course of the disease once called leprosy), the result of which is the decaying, corpse-like appearance of post-mutation humans.