We are currently facing an issue that when generating a feed for a German store, the attribute labels in "FilterAttributes" are in English. We are a bit behind in the version (v4.4.0) and we have customized the export quite a bit. As far as I can tell compared to the current version the feed generation has not really changed but we will try upgrading. As for the customizations, we are also using Omikron\Factfinder\Model\StoreEmulation in order to emulate the store the feed is being created for, that's why I wanted to ask if you have seen such an issue before or have an idea what the cause might be.
We generate the feeds hourly via a custom cronjob. To make sure it is not due to any overlap with other cronjobs we have already moved it to a custom group and run it with use_separate_process set to 1.