The export with i18n introduce a new element : The group Lang
The group lang is an id of a translation of a document for exemple a document in english and its translations have the same groupLang ID.

Create a new document for a group lang :
If you want to create a new document for an existing groupLang. For exemple, I've created a document in english wich is my master lang and i want to import a new translation in french
You just have to add in your import zip a document with the filename new_$GrouplangId_$Lang (for exemple new_WKq0ph4AACEA4M9B_fr-fr.json)

Create a new groupLang with all its translation
You can also import a new group of translation by importing multiple document with an arbitrary goupLang setted.
For exemple if i want to import a new english document and its translation i will name my documents.