[Korean Phrase] I'm sorry, that's personal. 죄송하지만, 그건 사적인 일이에요.

Sometimes, people ask really private things in Korea. Even if they didn't intend it, you'll need to say that's not proper question to ask.

In that case, you can use this phrase :-) 죄송하다(죄송해요) : be sorry ~지만 : however, even if, but 그건 = abbreviation of 그것은 : that 사적이다(사적이에요) adj. 사적인 adv.

사적으로 : personal, private 일 thing 이다(이에요/예요) : be(is/are/am)...