Do you mean:
* What is IN Belgium? (This would ask about things located in the country of Belgium)
* What is BELGIAN? (This would ask about things that are from Belgium, like Belgian chocolate or Belgian beer)
* What is something in the BELGIAN language? (This would ask about words or phrases in the Dutch or French languages, which are the official languages of Belgium)
Let me know what you're looking for and I can give you a more helpful answer!