The reason why "Sirs" is not allowed? 'Sirs' and 'madams' used to be recognized as the plural forms. The use of ‘sirs’ peaked around the beginning of the 19th century.
Gentlemen it is.
I remember my first day in Paris after five years of high school French, and a friend wanted me to ask the concierge for the rest room. Do you think anyone explained to me why five minutes later the concierge was still laughing after I said “Ce gentilhomme désire savoir où est la salle de bains. “
They do sound very similar but the beginning of messieurs sounds literally as it is written → like the word mess in English. On the other hand, the beginning of monsieur as no real equivalent English sound → sort of like "muh". Listen to them here:
I think part of the reason why there are even discussion groups at all is that Duolingo can try to gauge the quality of their examples by the volume and conclusions of these debates, though.
It may be doing this nonsense intentionally but without pushback, it will not stop or change.
And so here we are. :y
I have been at this for a while and it actually gets worse with time. There are a number of other flawed examples here where better translations were discarded as time went on, and when you look at the discussions, discover that Duo goes back and forth between accepting a word and then mysteriously rejecting it later, only to readmit it again eight months on.
"Frustration" towards a learning block is something you can use to motivate yourself, absolutely. But when you are frustrated at a learning tool for being pedantic and screwy, the best you can do is vent (as we are here) and hope that it will adapt-- as it is wont to do, for the most part-- to correct these small but aggravating nuisances.
Did you ever watch a two-year-old on the brink of language acquisition? They call it "the terrible twos..." Really it's the miraculous twos, perfection of skills without teacher, text or test...Not without frustration, but the satisfaction will be all yours when you're done. Don't give up!