Hi,
In Joomla, a multilingual site will depend on the menu items and modules used. So the same with normal Joomla template, when you use JA Builder, you will need to have menu item for each language and associated menu item for others. And in each menu item page, you will add your own block / use module for associated language.
For example, if you have Home menu item for FR, you will create an associated Home item for EN. In case, you build a complete page with JA Builder for Home – FR, you can use import / export feature of JA Builder and export current page and import to the page you want to use. Then if you use module position in block added to the page, the module assigned to this position will show depend on the language settings you assign in module settings.
Regards