I've always been suspicious of people with two first names.

[Sysman]

Although not relevant to doodab's question, as he mentioned, I was going to add that double-barrelled forenames such as "Mary Lou" used in the US were probably once considered fancy and "Frenchified".

They tend to be more of a Southern US thing, or that's my impression. So maybe they originated in the 19th century from French influence in places like Louisiana.

Without looking it up, I think you are right about the Southern influence, and the French one too.

[Sysman]

possible, but how do you explain the rivers then ?
Here its River Thames
US its Potomac river
In France its just The Seine

Rivers are another kettle of frogs. In German at least, even the genders don't seem to have any rules - you've just got to learn each one.

In contrast genders of countries in French do follow some logic, I can't remember it exactly, but here's a map (green is masculine, purple is feminine).