The sentence "he speaks so quickly" is grammatically correct and can be used in written English.
You can use it to describe someone's speaking style or ability. For example: - He speaks so quickly that it's hard to keep up with him. - Despite speaking so quickly, he enunciates every word clearly. - His job as a radio host requires him to speak so quickly.
"He spoke so quickly and in such a pronounced dialect that I had great difficulty in following him, but the same phrases kept recurring all through his address like motifs in a symphony: the Marxist traitors, the criminals who caused the revolution, the German army which was stabbed in the back, and – most insistent of all – the Jews".
A slender, unassuming woman in her early sixties, with dark eyes and dense eyebrows, a fine jawline, and a dimpled smile, she volunteered a few observations about Fiorentino, but she spoke so quickly that Lumpe had trouble understanding her.
Tyrik, who is energetic and speaks so quickly he can be hard to understand, received the game as a gift from his stepfather.
She has a sandpaperish voice and speaks so quickly, with such an information blizzard, that it is miraculous that she has the chance to make friends at all.
He mentioned the situation in Darfur and Tony Blair, but he spoke so quietly and quickly it was hard to understand him.
He was, in truth, speaking so quickly, and mentioning so many names and concepts, that I was a bit confused by the argument — until I looked down at the paper where he had been drawing the complex flowchart of French dessert-making.
The workers spoke so quickly in the pub that he couldn't catch a single word.
It is only too easy -- but still wrong -- to speak so quickly of a coverup in view of these difficulties".
The woman spoke so quickly that I didn't have an opportunity to tell her that I didn't understand Greek.
Every line is delivered in a robotic, high-pitched whine, spoken so quickly that you are left straining to keep up.
"Policemen never thought that history would speak so quickly to prove the complete innocence of the policemen in the events of the January 2011 revolution," said the spokesman, Hany Abdel Lateef.
