A language reflect the culture of where the language is spoken. If in English culture there is no such as the Indonesian ulture 'arisan', it will be very difficult to find the word for it. How would you say 'slametan' or 'tumpeng' in English. Even the Indonesian concept of 'mandi' cannot really be translated into 'having a bath' or 'taking a shower' because they are all different thing.
Why don't you just say arisa, then you can give some explanation after that. From then on, you can safely say arisan or 'arisan activity / gathering' whthout making your English sound funny.