"The youth is cheerful."
Translation:Młodzież jest wesoła.
so "youth" is always female gender, even when its a male?
(My answer was "Młodzież jest wesoły" and it got marked wrong)
it is collective noun, like "rodzina"( or not, there is no plural) and it is always feminine.
There is plural for „rodzina” – „rodziny”. Or did I misunderstood your comment?
After reading the comments here and on another exercise in this lesson, I am still very confused. If młodzież is always a collective noun, then I think the English translation should be "The youth are cheerful" - because we are talking about a group of young people - but maybe I still don't understand.
Both 'is' and 'are' are accepted, it is an American vs British English difference.
You are correct that there is a difference in handling collective nouns between American and British English. However, as in all things grammatical, it's a bit more complicated than that.
This blog article explains it well: http://englishasitisbroken.blogspot.com/2007/09/collective-nouns-what-are-they-family.html
Toward the end of the article they discuss collective vs. countable nouns, giving youth as a specific example. This Duolingo exercise is using youth as a collective noun, so it should only take the plural verb in English. By giving "The youth is cheerful" as the translation, you are implying that "the youth" is referring to a single individual.