Stopping acting like a baby! Pull yourself together!
别耍孩子气了，振作起来。

Pull oneself together 常用在口语中，意思就是重新振作起来，镇静下来。

Chin up! Only two exams left.
别垂头丧气的！只剩两门考试了。

Chin up或者keep your chin up 就是别灰心，别气馁。当别人处境困难时，可以用这句话鼓励。

Be prepared for a rough time. And hang in there.
准备吃苦，坚持下去。

Hang in there 别泄气，坚持下去。当朋友想要放弃的时候，说这句话，让他们咬牙坚持下去。

I'm sure it'll work out.
别担心总会有办法的。

Work out（某种事情）有效的，切实可行，成功。比如：The plan worked out badly. 计划实行得很不成功。

You can do anything if you really want to. That's the spirit!
只要你想做，你就一定能做得到。那才是好样的！

That's the spirit! 用于鼓励他人的勇气、决心，意思是那样才对，那才算好样的。