It seems that the slight delay is not wrong. Of three native speakers on Forvo, two of them seem to say it the same as Duo (with the pause), and the one that pronounced it without any slight pause in the middle got down-voted and the others got up-voted. The one who got down-voted was from Austria and the others from Germany. Perhaps some native speakers would like to tell us if this difference is a regional one or just a difference between the individuals concerned.
And 'modem' is short for 'modulator / demodulator', but like 'luncheon' it sounds rather old-fashioned or pretentious.
Luncheon is also more formal than a simple lunch- both the word itself and the act. The usage is not exactly the same. It's used to either describe something more formal than the typical lunch, or to describe a typical lunch formally. As we lack a real formal register, using it this way in English sounds a little haughty nowadays.
Let's allow the Oxford Dictionary to have the final word on this:
While luncheon can be more formal, lunch is still a shortened form of luncheon. And extent to which luncheon is still used depends on the region. That also influences to what extent it might sound "old-fashioned or pretentious." It certainly doesn't sound like either where I am from and usage is still frequent, although it is generally used in a more formal context. This still means that luncheon and lunch may be interchanged without affecting meaning, although it might sound slightly odd in context.
You're absolutely right on regional usage.
However, Duo teaches regionless Standard American English. It also accepts answers in UK Standard English.
Dialectal variations, however, are not standard- they are, in fact, why standards exist in the first place.
Differences based on regional speech cannot be applied to courses, otherwise there's no difference between Duo accepting your use of 'luncheon' for 'lunch' my Yorkshire 'thee' and 'tha' for differing froms of 'you', or constructions such as the Cameroonian English 'detailly' for 'in detail'.
If non-standard dialectal usage has to be accepted, we have to accept it all- minor or major.
'Luncheon' and 'lunch' have separate meanings in both standards. That's all that this course is concerned with. I'm not allowed to answer the EN -> DE questions in Bairisch or Plautdietsch, and I can't answer the DE -> EN questions in Weegie or Jamaican Patois.
It really is an uncommon word. It doesn't make the top 10,000 most common words in English, and in the last 200 years of English publications, it appears drastically less than 'lunch'.
This link: goo.gl/vzsJN1 gives an Ngram comparison of the frequency of both terms from the last 200 years of literature and written news.
They used to be quite even, but 'lunch' is now considerably more common.
Narrow the search to recent years, and the results are even more profound.
I believe we'll have to continue this on our profile pages, as we appear to have run out of space to comment.
The thing is that the definitions of lunch and luncheon vary only slightly in standard English English. I do not claim that their usage is identical, it is not. But their meaning is identical, and the usage of both common enough, that, without further context, they are perfectly interchangeable. Both English and American English use the word and it is purely regional usage that differs and makes the word luncheon seem, in your region, unusual or old fashioned.
As the OED definitions I linked you to show, they are not identical in meaning. Both imply organised midday meals, but one is formal, and the other is not.
I'd like to compare 'ball' and 'dance', as their use is very similar to our discussion. They both mean 'a social gathering for dancing', but one is considerably more formal than the other.
The same nuance is present in Standard English between 'lunch' and 'luncheon'.
All balls are dances, but not all dances are balls. In the same way, all luncheons are lunches, but not all lunches are luncheons.
Their meaning is not identical, but I have to agree that given no context, it should probably be accepted, even though it's an extremely uncommon word in Standard English.
Yes, pretty much.
So theoretically, it should have been respelled "Mitttagessen" in the 1996 spelling reform, but they left it alone because Mittag is no longer felt to be a compound of Mitt(e) + Tag.
(Similarly, ein Drittel stayed the same rather than turning into ein Dritttel, also because the Teil second component has been reduced to -tel.)