完食って英語でなんて言うの？

I devoured it! It was delicious! - Devour is to eat absolutely as if you were hungry & ate quickly. Normally used for a nice meal.
"How was your meal?" - "It was delicious! I devoured it!"

Gobbled it all up! - I use this for the second person, as like a child to eat all of their food/milk. "She gobbled all that up quickly."

I'm stuffed! - You don't necessarily have to finish the meal, it is just expressing that you physically cannot eat anymore & generally quite enjoyed it!
"Any room for dessert?" - "Oh no, I couldn't. I'm absolutely stuffed!"

This way you can express a positive feeling about the meal and because you ate it all.

These expressions portray that you enjoyed your meal, that is why you ate all of it.

1. To scoff = to eat quickly
2. It didn't touch the sides = the food/drink did not touch the insides of your throat (as it was swallowed so quickly - like dropping a stone down a mine shaft).
3. A swarm of locusts typically eats everything in its path such as fields of crops.

I didn't leave a drop.' - This is usually if your food involves soup or gravy and it means that you didn't even leave a drop of grave/soup. In other words, you cleaned your plate.

'I cleaned my plate.' - This means that you didn't leave anything on your plate. It is practically clean.

Both of these sentences express that said person has eaten all the food on their plate.

Sometimes we are so hungry we are said to: "wolf down" our food!
And we clear our plates...by polishing it all off in one go!
We are likened to ...eating like animals with no restraint ;-))
we "Pigged out" is another favourite... or eating" like a gannet! "
(a bird that swallows fish whole)

This expression is used to express that all the food on the plate has been eaten

Clean - used because the plate will almost resemble a clean plate after all the food is eaten
_
Example
A: Did you enjoy your meal?
B: Yes. I cleaned my plate.

A: I see that you cleaned up your plate
B: The food was delicious.

When we finish all the food on our plate it is a great compliment to the cook because it means that you enjoyed the meal.
If you would like to express that you finished your whole plate of food, use the sentences above."

"I ate everything on my plate, I might as well have licked my plate clean."
This means that everything was eaten, the plate looked as clean as it was before it had food placed on it.