Some languages are meant for singing, others not. A huge generalisation of course and it depends on what mother tongue you start out with. But there is a grudging consensus about Italian (and Welsh, but that's another story). Take this Handel aria:
Ombra mai fu
Cara ed amabile
Never was there a shadow
Sweeter, more refreshing
Or more gentle.
Yes, I know vegetabile looks a bit weird, but it doesn’t matter. You don’t have to know the tune – lovely and simple as it is – you don’t have to know the words are Italian, to realise that those syllables are easily singable and that they receive their stresses gracefully.
Contrast that with the second of these two lines from the French national anthem:
Entendez-vous dans les campagnes
Mugir ces féroces soldats?
Do you hear, in the countryside,
The roar of those ferocious soldiers.
I have spent half my life trying to learn French and adore its quirkiness. But that conglomeration of Ss between ferocious and soldiers (Even English sounds better!) requires gymnastics from the singer. And there’s worse.
One aria from Carmen (not my favourite opera) ends with Yes, I love you (Oui, je t’aime.). There’s so little in those vital words for the composer to hang his melody on. No resonances. As luck would have it I went on to play versions of the Queen of the Night aria from Magic Flute and the German for My Dear Son stood out: Mein liebe Sohn. (the Queen yearns achingly here). So much easier for Mozart than if she’d been French, singing Mon cher fils.
Here’s how ITALIAN (with help from Handel) wins every time