They might be saying that but it does not tally with my experience. I have met some very intelligent people who believe that the voices that they hear are being produced by an external source. Of course my subjective personal experiences of working with people with mental disorders does not count for much in the grand scheme of things but I have not noticed a general tendency for voice hearers to be markedly less intelligent than 'sane' people.

Inventing 'gibberish' words is a recognised symptom of psychosis called neologism. It is actually quite rare even amongst people who are very psychotic, in my experience.

Mental disorder is not the same as personality disorder. I am pleased that you found medication useful but the statement that there is no effective medication to treat personality disorder is correct