Let’s assume you have never visited China, and have no plans to do so. If I asked you in English, ‘Have you visited China?’, what would you say? Probably just “no,” which in Indonesian is tidak. In Indonesia, however, you would not say tidak in this case. You’d use a different word: belum. Belum’s literal translation is not yet.
To give another example: If I asked if you had eaten gado-gado, a traditional dish with vegetables and peanut sauce, you would answer belum for not yet. The only exception would be if you were, say, allergic to peanuts — and so you would say tidak for “no” and probably specify that you cannot ever eat peanuts or you might die. Otherwise, even if you have never considered eating gado-gado and you live in the U.S. where it would be difficult to find, you would still say not yet.
I like to think of this as a difference in outlook. No is very final. But life is full of surprises. You never know when an Indonesian will invite you for dinner, or when you’ll win a free trip to China. So just say not yet. (Others view this as a way to avoid confrontation, which is very important in Indonesian culture, but that is a topic for future posts). In any case, you might end up doing something you never expected to, and you’d hate to negate the possibility with a no. I like to think that’s the idea behind the heavy use of the word belum instead of tidak in Indonesian language.