> "Zéro est le seul nombre qui est à la fois réel, positif, négatif et imaginaire pur."

From: https://fr.wikipedia.org/wiki/Z%C3%A9ro#Propri.C3.A9t.C3.A9s...

It's hard to be more explicit that it is considered both.

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Added in edit

In speaking with a French colleague, he says that "inférieur" often means "less-than-or-equal-to" rather than "strictly-less-than", so the passage you quote would still imply that 0 is negative (and most likely also positive).

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Second edit:

> In France, "positive" means "supérieur à 0", and "supérieur à " means "greater than or equal to". Similarly, "négative" means "inférieur à 0", that is "less than or equal to 0".

> (We have the similar reaction towards the anglosaxon world and the introduction of nonnegative…)

-- https://mathstodon.xyz/@antoinechambertloir/1153275891164575...