胸有成竹的英文：
[Literal Meaning]
at heart/have/complete/bamboo
to have complete bamboo on one's mind

[解释]
在做事之前已经做好了计划和决定。

[Explanation]
to have a well-thought-out plan before hand

[例子]
如果你已经胸有成竹，就放心大胆地干吧。

[Example]
If you already have a well-thought-out plan before hand, do as you will.

[英文等价词]
to hold the cards in one's hand
have a card up one's sleeve
have an ace up one's sleeve
in the bag
know all the answers

Mr Smith always has a card up his sleeve.
史密斯先生总是胸有成竹。

He went into the trial full of confidence because he knew he was in the clear.
他胸有成竹地接受审问，因为他自己知道是清白的。

You must be certain of your facts before you start flinging accusations(around)(at people).
必须对实情胸有成竹才能理直气壮地(到处)指责(别人).

He looked down at the long, wicked blade
他低下头去，看看这寒气逼人的长刀锋，胸有成竹地啪一声把刀折叠起来，放回衣袋。