I assume you want to marry in Indonesia? It’s necessary for both partners to have the same religion in Indonesia to get married. And there’s always a religious ceremony before the civil registration (which is illegal in most western countries).
Obviously that does not mean you have to convert. Anyway, if that’s the choice you made just visit the temple of your future spouse and talk to the monks/pandita. (Or have her make a visit before that.) I realize that’s not necessary for a conversion to Buddhism but you need some evidence and make arrangements for the ceremony anyway.