Are you sure about the French phrase for it? My French is pretty non-existant but a German 'Darlehensvertrag' which I think is what you want, is, according to my good friend Leo, 'contrat de pret'. There are quite a few examples of contracts
in German on-line, so if all EFers are on holiday and no-one around to help you, you could try Googling the French phrase and see if any likely-looking text comes up.
I'm not sure it has to be deposited anywhere - maybe just signed by you both and safe so that you have it if you need it. Lawyers, where are you?
And if this isn't any help, at least it 'bumps' your Thread so that others might see it.