Which flights can I use my gift card on?

Your gift card can be used on a flight offered in the country where it was issued. A card bought in France is therefore used to book a flight in France.

One card, one country

Each market has its own cards, and codes don't carry over from one country to another. A card therefore can't be used on a flight in another country: the booking is declined.

If in doubt

Just go by the country of issue shown on the card. As long as the flight belongs to that same country, your balance applies as normal.