Question

用英文翻译：“这是一个不能说的秘密”

要语法正确，语言婉转的

Answer 1

This is a secret which can not say.
This is a secret （that）can not say.
两种均可。

Answer 2

"This is a secret being able to not speak"

Answer 3

This is a secret can't be spoken out!

Answer 4

This is a secret that can't say