Vacation time is not something that government can force an employer to add on top of your salary, it is your salary, it is just a different way to pay you.
I don't know for sure about France but in many European countries vacation is by law on top of your salary, so you're still getting your normal paycheck when you're on vacation. I wouldn't be surprised if this is the case in France as well.
In Australia, many employees are on a government mandated award. This has minimum salaries, overtime payments and holidays - So if you are say, a waiter or a retail assistant, you know what your minimum conditions will be.
Most awards enforce a payment of 117.5% of your salary when you are on holiday (20 days + 10 days public holidays) because most people spend more when they are on holiday.