Translation:It is twelve o'clock and it is time to eat lunch.
Setting aside the strange grammatical bloat "it is" DL obvioulsy know nothing about Finland and lunchtime ;) :D
Well, the Merriam-Webster gives quite different meanings for those: https://www.merriam-webster.com/dictionary/luncheon https://www.merriam-webster.com/dictionary/lunch
The Cambridge dictionary calls luncheon a formal lunch, that is, these are, again, different.
I'm sorry, but how old are you? The same Merriam-Webster says that the first usage of the word lunch as a noun was in 1800. You definitely look younger.
So OK, in my 84 years (80+ of speaking American style English which does not = Cambridge standards) we seem to use the two interchangeably: “Let’s do lunch” often can refer to a nice restaurant (formal) meal or a sandwich in the park. And often Finnish lunch, provided by the business kitchen, is quite the biggest meal of the day (more formal than ‘grabbing a bite’ or takeout at the desk.). But anyhow, just being flippant....and may you have a great lunch!