[coronabarb]

From UC Davis - "Lacto-Fermentation is a metabolic process that converts sugar to acids, gases, and/or alcohol. Lactic acid bacteria breaks down a food and in the process lowers the pH of the food making it more acidic. Examples of this are cucumbers turned into pickles and milk turned into yogurt."

Since we are talking about fermenting cabbage, you would need to use salt to prevent bad bacteria from taking over before the acid is formed. Typically, you don't add acid first. If some kind of acidic starter is added, that would be a different process (although I've not heard of that method before).