It's a most joyful occasion.

那是最快乐的时刻。

It is a most joyful occasion.

这是一个非常快乐的日子。

His good mood fit in with the joyful occasion.

他良好的心绪与那欢快的场合很和谐。

They were singing and dancing to celebrate this joyful occasion.

他们唱着、跳着庆祝这令人欢乐的时刻。