He always wearing a happy expression.

他总是面带喜悦之情。

People would have flashes of happy expression.

人们偶尔会妙语横生。

Smiling is a happy expression of a body language.

微笑是一种表达快乐的一种身体语言。

She wore a happy expression even though she was having a stressful day.

虽然忙碌了一整天，她仍然满脸喜悦之情。