After adding operatic vocals to Gojira's rendition of "Ah! Ça Ira," a song popular during the French Revolution, she went on to sing a portion of Georges Bizet's Carmen.
From NME:
The heavy metallers performed ‘Ah, Ça Ira!’ (which translates to ‘It’ll be fine’), a song that was popular during the French revolution, during a segment titled ‘Liberté’ (in reference to France’s famed motto ‘Liberté, égalité, fraternité’) that celebrated one of the most famous events in French history, as well as the nation’s emphasis on freedom.
Gojira appeared on the side of a castle surrounded by fire and bursts of red streamers to represent blood, with Viotti later appearing on a moving prop boat. Their performance followed a portion dedicated to Les Miserables and came just after a beheaded Marie Antoinette was shown singing.
Traditional lyrics translated at wikipedia (linked above) Gojira's lyrics translated via redditors:
Oh. It'll be okay, be okay, be okay,
Hang the aristocrats from on high!
Oh. It'll be okay, be okay, be okay,
The aristocrats, we'll hang 'em all.
Despotism will breathe its last,
Liberty will take the day,
Oh. It'll be okay, be okay, be okay,
We don't have any more nobles or priests,
Oh. It'll be okay, be okay, be okay,
Equality will reign everywhere,
The Austrian slave will follow him,
To the Devil will they fly.
Oh. It'll be okay, be okay, be okay,
To the Devil will they fly.
I was just casually watching opening ceremony without giving a shit before, waiting for my country flag to appear and out of sudden there's metal performance. Wtf? That's great! I look at the drummer and think "This must be Gojira!" And indeed it was.