I have had patients who, because of a stroke, have damage to the language areas of the brain. Note the plural - areas. The receptive and expressive language centers are separate although closely linked. I have had patients who are able to follow commands, thus showing comprehension of language but whose speech is disrupted at levels ranging from difficulty using the correct word to total gibberish or even complete silence.
I have also had patients who lose the ability not only to speak but to use any symbolism including pointing or pictures.

I am not sure how this fits in with any of the aforementioned theories of language but the human mind, as well as the brain interest me.

Oddly enough it is not unusual for a patient who speaks 2 languages to lose the second and rvert to the first language of childhood even if they have not spoken it for years. One elderly woman had to start learning English from scratch because neither her husband of 50 years nor her kids spoke any French.