First of all, German being the lingua FRANCE is very ironic
Well, Have Germany to win WWI, and apart from some minor wars, there is no world level war after that, and the German bloc survives until modern day
The German victory resulted in a white peace with Britain, Brest litovsky in the east and some colonial concessions from France, plus a friendly government in Belgium
Under those circunstances could German replace english as the lingua franca?