The author just probably like Leibniz a lot and prefer to make the citation in the original language of the text.
Would you have preferred Latin or German ? Leibniz used them too.
Would you have preferred Latin or German ? Leibniz used them too.
I could get by with German, but that's beside the point: the essay is written for an English-speaking audience, so it's stupid to insert extended passages of foreign text without providing translation.