I would probably be doing the same thing that you’re doing, digging through code.
I did some looking and I’m finding the information on imports for WPML quite confusing. In some places it says that the posts in the different languages is stored in alternate posts and in other places it says that the information is stored in a separate WPML language table.
The import plugin I mentioned I believe stopped supporting WPML to be honest. But I changed the name of the file you attached to .xml and I was able to upload the file and it understood it, but getting it to work would probably be another story. I’m still a little confused about why it imports the wrong data.
Sorry I couldn’t help more.
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