What is the author's style in Flashman and the Redskins by George MacDonald Fraser?

Flashman and the Redskins is told in British English. The narrator is an octogenarian writing about his life and career early in the 20th century, but the events described fall in 1849/50 and 1876. The novel is rich in the dialect of British soldiers, American woodsmen, Caribbean slaves, Mexicans, and various Native American tongues. Flashy claims to achieve fluency in Sioux, the lingua franca of the American West, which he finds lovely, but so hates the Apaches that he cannot bring himself to learn their difficulty and ugly language.