Steps to reproduce:

1. Create headless (name) folder under Ibexa Digital Experience Platform content and get it's location ID (i.e ID = 57).
2. Create ger-DE language.
3. Set up the following config:

           site:
               languages: [eng-GB, ger-DE]
               content:
                   tree_root:
                       location_id: 57
   

4. Enable the Site Factory.
5. Create new site in Site Factory (name it "Test", set parent location to Ibexa Digital Experience Platform, set standalone domain and select ger-DE language).

Result:
After going back to the Content Tree you will see "Test" content created in eng-GB language.

Expected result:
"Test" content should be created in ger-DE language.