如何用英语翻译“心有多大，舞台就有多大”？how wide your mind is , how big the world is 好不好？

可以的，“心有多大”其实用"How ambitious you are"更好一些。

差不多吧，我觉得The wider your mind is , the biger the world is
更好些

直面翻译：How large the heart is,how large the stage is!
意译翻译：Nothing in the world is difficult for one who sets his mind to it!(世上无难事，只怕有心人）
心有多大，舞台就有多大：就意味着只要有信心，就能成功