中秋节吃月饼的英文表达是"eating mooncakes during Mid-Autumn Festival".
关于中秋节吃月饼的来源，传说有很多，但其中最常见的是与宋朝的故事有关。据说在宋朝的一次叛乱中，有一个人把计划写在月饼上，通过吃月饼的方式传递消息，从而成功地解放了长安城。从此以后，吃月饼就成为了中秋节的一种重要传统。
一些英文例句及其中文翻译：
During the Mid-Autumn Festival, it's a tradition to eat mooncakes with family. (在中秋节，和家人一起吃月饼是一种传统。)
Mooncakes are a symbol of reunion and togetherness during the Mid-Autumn Festival. (月饼是中秋节团圆与共聚的象征。)
Giving mooncakes as gifts is a common practice during the Mid-Autumn Festival. (在中秋节送月饼是一种常见做法。)