Many historical oeuvres are known by multiple names and/or multiple variations of each name. For example:
The title of Thomas Malory's Le Morte d'Arthur was originally written as Le morte Darthur, inaccurate Middle French for The Death of Arthur
Jeoffrey of Monmouth's Historia regum Britanniae (en. The History of the Kings of Britain) was originally called De gestis Britonum (en. On the Deeds of the Britons)
La mule sans frein is also known La demoiselle a la mule (en. The mule without a bridle and The damsel with the mule)
Les actions des rois d'Angleterre was originally titled De Gestis Regum Anglorum
and so on
What is the way (or multiple ways) to decide which of these titles to use in your own work when you citing, referencing, or simply discussing these works?