First, an author who produces some good dialogue is Harry Turtledove. The master himself has a huge library of alternate history, much of it dialogue driven. My suggestion, read In the Presence of Mine Enemies, especially the first chapter. A family meets for dinner and for one little girl this is a very special night since she gets to stay up late for the first time. For the family, however, it is much more significant. This is the night they tell her she is Jewish. By the way, the year is 2010 and this is the Berlin of a timeline where an isolationist America stayed out of World War II until it was attacked by Germany and Japan a generation after the fall of Britain and Russia.
I did receive other suggestions for examples of good dialogue in alternate history works, and here they are:
K is for Killing by Daniel Eastermans: Where the Ku Klux Klan takes power in the United States in 1932.
SS-GB by Len Deighton: Suggested to me by Hugh Ashton, who also suggested you check out his novel Beneath Gray Skies.
Then Everything Changed by Jeff Greenfield: While most of the novel reads like a history textbook, there some scenes of dialogue between historical characters that may prove to make an interesting radio play, like LBJ talking with his advisers during the Cuban Missile Crisis.
Tunnel Through the Deeps (or A Transatlantic Tunnel, Hurrah!) by Harry Harrison: Atomic locomotives, coal-powered flying boats, ornate submarines, and you talk all of this using Victorian dialogue, sounds awesome to me.
Watchmen by Alan Moore: A graphic novel, but the dialogue between the characters in this excellent story about masked vigilantes is still amazing.
The Yiddish Policemen's Union by Michael Chabon: A detective novel set in a Jewish homeland in Alaska. Think of it as the Lower East Side in the Great White North.
Protect and Survive by Macragge1: I am told this work has excellent "internal" dialogue.
Have anymore suggestions? Please leave them in the comments section.
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Mitro is founder, editor and contributor of Alternate History Weekly Update. When he is not busy writing about his passion for alternate history, he spends his time working as a licensed attorney in the state of Illinois and dreams of being a published author himself one day.