"나는 아들이 있으면 좋겠다."
번역:I wish for a son.
"I wish for a son." is not a very common expression. More common would be:
I want a son.
I wish I had a son.
I would like to have a son.
and yes, Philo, it's ok to insert "that" though unnecessary.
I wish that I had a son.
I'd love to have a son.
If I had a son, I'd be happy.
It would be so nice to have a son.
Dara, "I wish I could have a son." implies you are unable to have a son. 불가능한 The other sentences all imply possibility.
Philo, I don't have a good answer for why we use the past form "had" Sorry.