Currently, the REST API import is coded to accept one file at a time for import. To get a chance of future support for bulk import in the future Gainsight would need to have an enhancement request on the community.
This is the enhancement request to do a BULK REST API to allow a bulk import of localized language translation files (xlf,xliff).
I have some python code that will for an engagement spin through a file location and upload xliffs.
I would like to expand this code to allow a spin through by engagement and upload the appropriate engagement xliffs.
The better plan would be to get automation of the transfer between the langage provider and Gainsight. If anyone has done this or has any helpful comments, I will appreciate any help I can get on this.