There is no module position for main menu. Main menu is a static element in our templates. You can select which menu to use and animation style in template settings.
1. A default menu with default home element attached to language ALL (this menu can only have this one element) 2. Make Japanese main menu with default home element attached to Japanese 3. Make Portuguese main menu with default home element attached to Portuguese
When You will have menus ready. Make 2 copies of template style and select a different menu and language to show it for to both of them.
Unfortunately I cannot tell what is displaying and what is not, because of a language barrier, but please take a closer look to languages articles and modules are attached to and remember that different menus has different IDs so You need to attach modules to them separately.