Gah! This program is so frustrating -- why is "Happy holiday" not accepted?
Precisely. I suspect it's because the people (who've put in a lot of hard work) doing this course learnt their English in America. "Happy Holidays" is something one hears in the USA in December to avoid favouring any particular religion. But in a general sense, outside the USA, one could hear 'happy holiday'.
Do people actually use this? In what context, is it Spring Festival plus some others? Or is the pluralization misleading?