Quoting Jefferson's letter from link:
I have made enquiries on the subject of the negro boy you have brought, and find that the laws of France give him freedom if he claims it, and that it will be difficult, if not impossible, to interrupt the course of the law. Nevertheless I have known an instance where a person bringing in a slave, and saying nothing about it, has not been disturbed in his possession. I think it will be easier in your case to pursue the same plan, as the boy is so young that it is not probable he will think of claiming freedom.
Obviously, we are talking about France - not about its then colonies in Haiti or Louisiana. The French law for France dates from the Christian Queen, indeed a Saint of the Catholic Church, Bathilde. Actually it is from before France, Germany, Savoy, Benelux etc. split up - so it was valid in these other European countries as well. St Bathilde was a Merovingian Queen. Merovingian and early Carlovingian Francia is larger than just France.
The laws for the colonies like Haiti and Louisiana were by contrast from the era between Renaissance and Enlightenment, between acquisition of colony and French Revolution.
Germany, meaning back then Holy Roman Empire, and including populations not speaking German, of which Prussia and Austria and Bavaria and Bohemia were four states, and of which the Austrian Archduke and Bohemian King was regularly also Emperor, obviously also had the laws of Queen St Bathilde.
But unlike France in the later Capetingian sense, the Germanies, the Holy Roman Empire, had not acquired colonies overseas. And therefore they had no colonial laws like those corresponding to the French legislation of Haiti or of Louisiana.
Speaking of the latter - during a period of La Régence (1715-1723) or of Louis XV's personal rule (1723 - 1774, not sure now which of the two) laws got worse for blacks in Louisiana. Before, a free black man had had the right to carry a gun, like a free white man. Afterwards it got better again, and I think USA Louisiana and CSA Louisiana was one of the slave states, perhaps the only one, where a free black man could carry a gun, precisely as a free white. I think this amelioration already happened before the French Revolution and before France sold Louisiana (or before Napoleon illegally occupying royal functions in France sold Louisiana) to the United States.
Early Middle Ages - a time when slaves get freed in the heartland of Western Europe. Early Modern Times - a time when Europe's West Coast countries acquire colonies - and slaves.
Hans Georg Lundahl
St Mathias Apostle
And recent times : when Mauritania still retains its slaves.
AFK Insider : 12 African Countries With The Most Slavery : 1. Mauritania – 4% (Worst in the world for modern-day slavery)
By Keren Mikva AFKI Original Published: January 29, 2015, 8:15 am