'occidentalise' originates from French, specifically the word 'occidentaliser', ultimately from Late Latin 'occidentalis', where 'occidens' meant 'west' (literally 'the setting [sun]').

'occidentalise' changed from French 'occidentaliser' (and before that from Late Latin 'occidentalis'/'occidens') and was borrowed into English as 'occidentalise' (with later parallel form 'occidentalize' in US English).

Initially it referred to things 'of the west' or 'western', but over time it evolved into the verbal sense 'to make something Western' (to Westernize).