Hi,
Regarding your currency question, you cannot do it like that. HikaShop would not be able to work like you want because what would happen if a user where to select one product for europe and another one for asia ? Or if his address would actually be not in the same zone that he selected ? So it's not a possible solution.
Usually, you either have the currency switcher module so that the user can select his currency, or your have the geolocation plugin setup so that it selects the currency automatically based on the location of the user. Then you can simply restrict your payment methods based on the zone of the user.
Falang is not mandatory. You can have HikaShop's interface translated simply by having the translation files of HikaShop present and for the HikaShop content, if you do like joomla and you create one set of categories/products for each language and assign each top language category to the corresponding menu of the joomla menu manager, you'll be able to have your content translated as well.
If you want to avoid the duplication, then Falang would be necessary, but it can work fine together with the native joomla language system.