Did French ever have any special status in Austria or the Austrian empire, akin to it being the language of royalty in England (and possibly Russia, I'm not sure) (as opposed to it being just another foreign language)?
France and various Habsburg lands including Austria were political and diplomatic enemies and often at war during almost 300 years from about 1477 to about 1750, and again for most of the French Revolutionary and Napoleonic Wars.
During that period French became the most prestigious living language in western Europe and was a second language to most members of the social elites. But Austria seems like the realm whose government had the least motive to decree any sort of special favorable legal status for the French language. So I doubt that anyone will find much evidence of a special legal (as opposed to social) status for French in Austria, however Austria is defined.