Using Feeds to import multiple languages
Import from two xml files (on for each language), my empiric solution  :


I created two feed imports.
I forced the language field for each one.
Two separated nodes were created for each content (one in each language) but it didn't links the translations.
So I used a SQL query to finish the job, it's based on the feeds uuid


Note: In order for this to work your GUID must match between the two sources. If you have set that to the node title it is important that you turn off the option to replace content as it will update the previous import :/

UPDATE
    node n,
    feeds_item lng1,
    feeds_item lng2
SET
    n.tnid = lng1.entity_id
WHERE
    (
        n.nid = lng1.entity_id
        OR
        n.nid = lng2.entity_id
    )
    AND lng1.id='feeds_importname_for_lng1'
    AND lng2.guid=lng1.guid
    AND lng2.id='feeds_importname_for_lng2'