I've never known that this saying exists... that could be, however, if you don't think of the idiom it's good comic relief (so random). For some reason I doubt this because this is the Dates and time skill. It should be in the Idioms and proverbs bonus skill, so I bet it's just qualified for the skill because of the word "dejeuner".
You should probably avoid synonyms. The drop-down menu didn't suggest "dinner"
"Dinner" in France (or some parts of it) is the evening meal.
In Australia, for example, "dinner" is the main meal served in the evening, but some Aussies prefer to refer to that meal as "tea". Other parts of the world call the evening meal "supper."
I guess I'm saying that you can't expect Duo to accept all regional differences within the English-speaking community, or where usage of that word causes a conflict with their own definitions.
I'm not suggesting that Duo should offer it as a suggested translation, but it really does frustrate me that these questions never accept "dinner" as an answer, even though it's not really incorrect. Whenever I get one of these questions, my first impulse is always to write "dinner": it's the word i would ordinarily use in day to day speech (the evening meal is "tea"), and furthermore, it looks a lot like "déjeuner". This nearly always trips me up, especially in the timed exercises when i don't have time to think 'oh, but Duo expects me to call it "lunch"', and yet i know the meaning of the French word.
I guess i could keep losing points and hitting "my answer should be accepted", but i think it would be ignored, so i'm just kinda venting here.
Outside of France, "déjeuner" is breakfast; in Belgium, Canada, Switzerland, and Congo, "dîner" is lunch; and in the first three countries, "souper" is supper. In France, "dîner" is an evening meal and the main meal of the day, and "souper" is a light meal eaten at night (later than dîner). The more you know.
My teacher said this is because the French don't usually eat a heavy breakfast. It's more of a snack than a real meal. -> http://www.healthguidance.org/entry/15260/1/What-Is-a-Traditional-French-Breakfast.html
Luncheon is the term that was used in Tudor England and has more historically been used among aristocracy within the UK. It is still used today though usage has decreased somewhat. However I have known it to be spoken sometimes as a mock to the upper classes and other times just because. It is said by many people still today though more commonly the mid-day meal is known as 'dinner' or in colloquial English, 'lunch'.
I don't know who the hell would say "You eat my luncheon!". A "luncheon" is a group of ladies having lunch together at somebody's house for some reason. There has to be some reason. You can't just have a "luncheon". Perhaps your wife's bible studygroup might have a "luncheon" Don't ask me what they do there. I have no idea!
Technically no one would say "You eat my luncheon", you would have to say "You are eating my luncheon". In addition, the word "luncheon" actually saw a slight peak around 2010 though this was not as high as the middle of the first half of the 20th century. I have known it to be used several times and as a GCSE student I can quite safely say that none of those occurrences have been to do with "a group of ladies having lunch together at somebody's house for some reason" plus that is rather sexist in our modern day equal society. In society generally luncheon is actually used less rarely than you may think.
I find "luncheon" sorta funny. Like it's not wrong, but, if you're gonna say it, you have to put on your daintiest posh person voice and stick out your little finger while sipping your piping hot Darjeeling.
It's right that Duo accepts quirky synonyms like this. Who knows, maybe the queen will take this course, i'm sure she'd be frightfully put out if it wasn't accepted, what!