I'm not 100% sure about this, but I think you must retrieve the translated labels/objects/etc., along with the translation metadata for them to be populated. I think they're a bit like permission sets in that regard that they're populated based on the related metadata that's included in the same retrieval request.
If expanding the retrieval to include the translated metadata as well doesn't resolve the issue, I'll likely need to get some debug logs from you to see what else might be going on.
Regards,
Scott Wells