Many Chinese believe in an old saying, "Content is happiness."

很多中国人相信一句老话，“知足常乐。”

The happiness from helping others is a kind of inner relief or self-soothe, or the content of our heart.

我们得到的是，心灵的平静，助人为乐的快乐，当然也有可能是内心的解脱，或者自我的安慰，心灵的满足。

One nightingale sang at her heart's content: happiness is priceless.

夜莺尽情歌唱着幸福无价。

The secret to happiness is being content with what you have.

使你幸福的秘密是满足现在你所拥有的。

Happiness is a feeling, not content, never happy.

幸福是种感觉，不知足，永不会幸福。