Question

是at spring festival 还是at the spring festival

Answer 1

都不是，这句话中文理解为：在春节期间，所以正确应该是：during the festival 。
例句：
1、During the festival, unmarried girls joined a foot race in three age groups.
活动期间，未婚的女孩分成3个年龄组参加赛跑。

2、Traditionally, those living apart from their parents return home during the festival period.
传统上，这些远离父母的人在春节期间回家。

3、The rest of us are interested in resting in the restaurant during the festival.
在节日期间，我们其余的人对在餐馆里歇息感兴趣。

Answer 2

我国节日前一般均有定冠词，严格来说是 in/at the Spring Festival
但实际上 in/at the Spring Festival也是可以的

两种都指在春节期间

拓展
in every Spring Fastival 即每逢春节。

Answer 3

应该是at spring festival.