Quote Kosh="Kosh"
You're aware that foreign languages get translated into English, yes? Guess what the English translation for the midday meal is.
'"

Er, first it doesn't need translating. "The midday meal" is already in English.
But OK, let Google translate do some random translating, and see what it turns up:
Quote KoshPolish:
OBIAD
dinner
noun
1. dinner
2. midday meal'"
Hmm. Maybe Google Translate is just doing that to spite you. Let's try another one.
Quote KoshEstonian:
lõuna
south
noun
1. south
2. lunch
3. dinner
4. luncheon'"
Quote KoshNorwegian
middag
1. middag'"
Quote Kosh="Kosh"Words and their usage change over time. The question asked was not about the origin of the word, but about usage.'"
You can get as indignant as you like, but there is no universal usage, or universal answer, and I think my view - that much depends on the size of the meal, and when the eater has their main meal of the day - is fair and accurate.
Your point about translations is in fact disingenuous, as any translator, when faced with the word for a given meal in a foreign language, will only provide a translation which is [ihis understanding[/i of the English equivalent. Which for obvious reasons will be heavily influenced by (a) who taught him English and their predilections and/or (b) whereabouts in English speaking lands he has lived (if at all). As my varying examples above clearly show.
But it's not just me. Somebody asked the question to Gareth Rees on the BBC learning site. This is what he had to say:
Quote Kosh="BBC's Gareth Rees"In the middle of the day, you might have lunch or dinner. Lunch sounds more informal or more typical, particularly for people who are working.
In the evening, you might have dinner or supper. I think that people who have a quick lunch in the middle of the day will say they have dinner in the evening and this dinner will be a good meal.
A supper is usually a light meal and is probably had after a larger dinner has been had in the middle of the day.
Confused? Well most people see a dinner as a more complete meal. A common lunch in England is a sandwich, but dinner might include soup, meat with vegetables, and then a dessert like apple pie and ice cream. So, dinner is really the main meal and people might have it in the middle of the day or in the evening. Lunch and supper are both light kinds of meal. Lunch is in the middle of the day, supper is in the evening. '"
I'm going along with that as the best answer of modern usage.