1. Open ShopFactory
2. Select Settings menu => Global Settings
3. Choose Settings for this website => Miscellaneous to only change this shop's settings.
Update "New website" as well if you want to use this feature in other shops in the future.
4. Locate "Automatic customer language detection" and tick it
(if the box is ticked it is turned on, if Unticked it is turned off)
5. Click Ok to complete the setup.
6. Republish your shop to upload the new settings