c'est l'heure de manger le gâteau
I don't think you would. It is not something the French would be inclined to eat. Having said that, lava is "lave" in French, and cake is "gateaux." So maybe "lave-gateaux"?
Gateau is food cake in french
A birthday cake in French is 'un gâteau d'anniversaire'
gâteau
We eat cake translates as Wir essen Kuchen.
A banana cake is "un gâteau à la banane" in French.
gâteau sucré
In French, you would say, "Puis-je avoir un gâteau, s'il vous plaît ?" This phrase translates directly to "Can I have a cake, please?" in English. It’s a polite way to request a cake in French-speaking contexts.
If you mean a slice of cake it is - tranche
gâteau basque.
acheter un gâteau
"Let them eat cake" is "qu'ils mangent du gâteau" in French. If you refer to the famous answer from the Queen Marie-Antoinette: "if they don't have any more bread, let them eat cake", the original quote is supposedly "s'ils n'ont plus de pain, qu'ils mangent de la brioche". While this is often used to illustrate the arrogance of aristocrats, it is now questioned that she ever said that.