Today (14 July) is France's National Day, known in English-speaking countries as Bastille Day, after the Storming of the Bastille on 14 July 1789 as seen in this drawing below, by the French painter Jean-Pierre Louis Laurent Houël (1735-1813).
In the center of the painting, you can see the arrest of Bernard René Jourdan, marquis de Launay (1740-1789) - the French governor of the Bastille.
From what I understand, the French people don't say phrases like "Happy National Day" or anything similar to each other during their celebrations. This has also been described by the blogger je parle américain a few years ago.
So instead, I'll simply say "Happy vacation" to all of you who celebrate the Bastille Day and I hope you have a great day!