From Wikipedia:

“The Diva Dance opera performance [from "The Fifth Element"] featured music from Gaetano Donizetti’s Lucia di Lammermoor “Il dolce suono”, the mad scene of Act III, Scene II, and was voiced by Inva Mula-Tchako, while the role of Plavalaguna was played by French actress Maïwenn Le Besco. As the character Plavalaguna is humanoid alien, her vocalizations seem beyond physical possibility; however, in a documentary feature on the Special Edition DVD release, it is claimed that Mula-Tchako’s voice was not digitally altered. Canadian vocalist Marie-Ève Munger performed the complete Diva Dance before a live audience, and her performance was later aired on Québec television as part of a promotion for a televised boxing event.”