>>13013393About the word "personne" and the double negation "ne pas", the explication is very simple. Initially there was only the simple negation "ne", as in the sentences "Je ne sais." or "Je ne peux.", but in order to clarify and quantify the negation, people started to add a word according to the action : "Je ne bois goutte.", "Je ne marche pas.", "Je n'écris point.". Ultimately, people started to dissociate the added word with its actual meaning, and for some reason it became a mark of negation and the word "pas" replaced the others.
That is why person can mean nobody : first people said "Il n'y a personne" to quantify the absence of person, so it meant that there was nobody, but to simplify, when someone asks "Qui y a-t-il ?", one can respond "Personne" to say "Il n'y a personne", hence "personne" also happened to mean "nobody".
To say money, French have the exact word monnaie, derived from the old French moneie which also gave the word money in English.
"Argent" is used because usually, money was silver coins.
For the numeration system, it is a residual of the ancient vigesimal way of counting which had a base 20 instead of a decimal way in base 10. It was "Dix, vingt, vingt et dix, deux vingt, deux vingt et dix, trois vingt, trois vingt et dix, quatre vint, quatre vingt et dix, cent", but when the decimal system came, trente, quarante, cinquante et soixante had more success.
