"What are you up to?" is an informal question in English that can be translated to "lagi sibuk apa?" in Bahasa Indonesia. It is often used as a conversation starter to ask what someone is currently doing or what is going on in their life. The question can be interpreted in different ways depending on the context and the relationship between the speakers. For example, it can mean "what are you doing right now?" if the person sees you regularly. In general, the question is not meant to be intrusive or demanding, but rather a way to show interest and start a conversation. When responding to the question, it is common to give a brief update on what you are doing or planning to do.