You can import a new document along with its translations in one import job. To do this you need to use this file naming convention new_{groupid}_{lang}
groupid is an arbitrary identifier that will be used to match a new document with its translations. Just don't use the underscore character for this groupid.
Example, to import a set of localized pages in 3 languages, filenames should look like:
new_myimports_en-usnew_myimports_fr-frnew_myimports_es-es
When importing a set of localized documents, a grouplang ID will be assigned to the documents. The groupland ID is useful if you need to import more translations in this group later on.