18 carat gold nib model - for the French market

In the French market, only nibs made of 18 carat gold or more were referred as "gold nib" (Pelikan-collectibles)⁽¹⁾. So, Pelikan fountain pens were equipped with 18 carat gold nib for the French market. As the brand name, the French form Pelican (originally Pélican) were often used on the pen. Here are some models with 18 ct gold nib (model 100, 100N, and 400). Some nibs had imprints "Angleterre" or "England", while other nibs imprints "GERMANANY". Interestingly, as far as I confirmed, all nibs lack millesimal fineness (e.g. 750), different from 14 carat nib of the same time. Some pens have "Pelican" imprint on the cap top (see "Pelican" model).

Note;⁽¹⁾Many sources mention it, but I was not able to track down its primary (original) sources. Why 18 carat gold or more in France? Was that regulated by law, decree, or commercial practice? How long was it in effect?