In 1919 the German Fleet scuttled itself at Scapa Flow. One battleship was saved, SMS Baden, which was run aground in shallow water before it sank. The Royal Navy used the Baden for various tests from 1919 through to destruction in 1921.
Thats 'Real Life', how boring. Lets say the RN do tests on the ship through late 1919 early 1920, then cede the vessel to France who had been unable to complete any of its Normandie class battleships as the war had made other calls on resources. Frances best ships at the time were the three Bretagne class with 10x13.4, virtually obsolete when compared to the latest UK, US, and Japanese battleships. The parlous state of the French economy made completing any of the Normandie class ships impossible. Receiving a ship like Baden for free would be of great value to France. With a ship of the class of Baden as Frances Fleet Flagship they would have at least one ship of true force.
Various upgrades like, changing the boilers from coal fired to oil fired, fitting of several 75mm AA guns, and later the first 37mm AA weapons. New optics for the rangefinding eqipment. etc. were fitted during the inter-war years.
Like the other ex-WW1 battleships of the same era, the French took the Verdun in hand for reconstruction on completion of the Dunkerque in 1936. With Dunkerque and Strasbourg being the latest French capital ships, superstructure and minor weaponry were copied from those ships. The Verdun returned to the fleet in very good order and well able to take on its peers.