When did the popularity (amongst all aristocracy) to speak French on a frequent basis begin and end?
In England the upper classes still spoke French (though not usually as a first language) as late as the 14thC; Chaucer describes the Prioress as speaking French – but only French as taught in her school; “The French of Paris was unknown to her.” This implies that French was a polite accomplishment, but not the normal medium of communication in the 1380s. As another responder points out, during (roughly) the reign of Louis XIV and the short-lived French hegemony in Europe, French gained local status (only in Europe; the Chinese and Indians had never heard of the language) and became the standard language of diplomacy and international affairs, much as English is now. In Russia and Germany French remained a spoken language among the upper classes until the 19thC; we find Mozart’s wife referred to as Madame (not Frau) Mozart in a letter, etc. The unification of Germany and the Bolshevik revolution sparked conscious nationalist movements to promote use of the local language for all purpose
