Did 李白 and 杜甫 popularize/standardize any 方言?
李白and杜甫 make the language of Shaanxi(陕西）popular.
They were the people of tang dynasty ,and capital of the tang dynasty is Chang'an where is in Xi'an of Shaanxi province now.So the language of Shaanxi is standard for everyone like the dialect of Beijing has effect on Chinese now.