Don't tell anyone.
だれにも言うな.
Please don't tell anyone!
Please don't tell anyone.
Don't tell anyone.
Don't tell anyone [say anything to anyone] about it.
Keep it to yourself [under your hat].
Don't say anything to anybody.
Don't tell anyone this.
Don't tell anyone this.
I told you not to tell anyone.
Don't tell anyone about this.
Who can say?
Never, ever tell that to others.