It's not uncommon in British English either. English literature is littered with characters remarking upon the good humour of themselves or others.
"Elizabeth took an opportunity of thanking her. “It keeps him in good humour,” said she, “and I am more obliged to you than I can express.”
~ Chapter 22, Pride and Prejudice, Jane Austen.
"Bessie sometimes narrated on winter evenings, when she chanced to be in good humour...."
~ Chapter 1, Jane Eyre by Charlotte Brontë
In my dialect, "I am of good humor" is wrong; it should definitely be "I am in good humor" (or good spirits). It's certainly less common than "I am in a good mood", though. Duolingo's translation is nonsense to me — it would mean that the speaker was composed of good humor, rather than saying something about his mood.
No, but you could say « Je suis de mauvaise humeur ». Take a look at this page: http://french.about.com/od/grammar/a/mauvais-mal.htm
Take it literally: "I am of good mood".
Now use that structure properly in English, with other examples: "to be of XXX descent / origin", "to be made of something" :
I am of Indian descent
It is made of silk
You wouldn't say "I am of the Indian descent" or "It is made of the silk". In French, it's the same : "Je suis de descendance indienne", "c'est fait de/en soie". We don't use the article, as we're not talking about a specific thing (humor, descent or silk) but it's an expression, all the words of that expression sort of form an adjective - and actually you could replace all those expressions by an adjective :
- Je suis indien (d'origine) / C'est soyeux / Je suis jovial (I am Indian / It's silky / I am jolly)
And adjectives (after "to be" or that type of verb) do not take articles. It's like you said "I am made of good mood", "Je suis fait de bonne humeur".
The same principles apply with other types of verbs, and when you can also replace the expression by an adverb:
- Il s'est réveillé de bonne heure (= He woke up bright and early) = Il s'est réveillé [très] tôt
Can someone explain why 'bonne humeur' sometimes means a good sense of humour, and sometimes a good mood? It seems to be pretty arbitrarily distinguished across a lot of questions here and I keep getting them wrong by picking the wrong meaning in the wrong place - e.g. here I put 'I have a good sense of humour' and got it wrong
Do not mix "humeur" and "humour": the former is "humor" as in "mood", "spirit", while the latter means "humor" as in "ability to laugh, make jokes, etc."
être de bonne/mauvaise humeur = to be in a good/bad mood
avoir le sens de l'humour / un bon sens de l'humour = to have the sense of humor / a good sense of humor