Actually the first time that this diplomatic power was associated with France was in Colonization (that was another great game from Sid Meier long long back in the nineties).
In Colonization France had diplomatic boni with the natives.
Apart from this I am one hundred percent convinced that this power is fitting throughout the whole history (if we exclude the Celts and just see the Frankish (French) from the Dark Ages onwards.
Lets see, France in XXI. Century is surrounded by allies and economic partners, has a good reputation worldwide. It has friendly relations and diplomatic influence in all former colonies (despite some nasty independence wars). It is hosting several multinational companies, it is hosting several institutions of world rank and has in general much more diplomatic weight than it ever should have if you just count the economy or military. That is not bad for the Grande Nation, which is actually a quite small country.
If there are any negotiations in Africa , who is invited ? France.
If anything important is happening in Europe, who is consulted ? France.
Talk about United Nations, about ECB, about the ESA (about Airbus), about the German Reunion, the Expansion of European Union, the Civil War in Balkans, the fires in Middleeast, Africa, South-East Asia and who is always in the boat ? France ...
And this just in XXI. and XX. century. In the XIX. century France had even more diplomatic influence, actually being the second largest colonial power, not to mention the Golden Age in XVII. Century or the French Revolution in XVIII. Century. Not to mention that France had its own Pope, that Charlemagne was French etc. etc. ...
We Germans always envied France and French lifestyle, but finally even we made our peace with them (at first forcefully, but then quite deliberately) .... and a nation that could appease the German Juggernaut has to have diplomatic skills !!
Besides .. imho Italy is actually the most beautiful country in Europe. It has simply everything : Ancient Ruins and Modern Theatres, Low Cost Markets and Luxury Shops, Street Cafes and poshy nightclubs, Sunny Beaches and Ski Resorts, wine of Toscana and the pizza of Napoli, Italian Cuisine and Italian Ice-cream, Michelangelo and Tutti-Frutti, last but not least Italian Women and Foreign Tourists

(dont know much about Italian men , sorry

) anything else required ?