Is it permissible to pay the Zakat on a son's money in France using Algerian currency, and is it permissible for him to take interest from banks under the pretext that he is not being raised among Muslims?

There is no objection to paying Zakat (definition) on behalf of one's son, provided he authorizes it. The majority of scholars hold that non-believers are addressed by the ancillary branches of Sharia (definition), and even if it were argued otherwise, usury (riba) is forbidden for both the receiver and the giver. The Prophet, peace and blessings be upon him, said: "The receiver and the giver are equal in it [sin]," and "The Messenger of Allah, peace and blessings be upon him, cursed the one who consumes riba, the one who gives it, its scribe, and its two witnesses, and he said: 'They are equal [in sin].'" Therefore, it is not permissible for the son to take interest from usurious money. If it has already been received, then the priority is to take it and dispose of it in charitable ways.