He appealed to his countrymen not to lose heart.

他呼吁同胞们不要灰心丧气。

《柯林斯英汉双解大词典》

This is not the time to lose heart.

因此现在还不是丧失信心的时候。

youdao

Not to lose heart, when we are in trouble.

当我们遇到困难的时候，不要灰心。

youdao

And any argument between us would not cause me to lose heart or feel a sense of loss.

VOA: special.2010.07.11

If that bank says no to you, do not lose heart.

VOA: special.2010.07.18

One such expression is to lose your heart to someone.

VOA: special.2010.07.18

But if you ever start to lose heart, I brought you all here today because I want you to think of each other.

WHITEHOUSE: First Lady Michelle Obama Addresses Young African Women Leaders | The White House

Hill made it three penalties out of three just after the hour mark, and with time running out, the visitors visibly began to lose heart.

BBC: Bristol 17-0 Stade Francais

This is not the time to lose heart.

ECONOMIST: The war in Afghanistan