Could you post your CSC code.
To locate your device's CSC, (Consumer Software Customization), code, go to...
Settings > About phone > Software information > Service provider software version (see screenshot)
Yes, sure enough, that is the CSC code for the unbranded Russian firmware which explains why it is coming up with Russian language on initial set up. It also means that you will receive the Russian firmware releases. This type of phone is known as a, "Grey Market", handset inasmuch as it is not intended by Samsung for sale in the U.K. My advice would be to return it and ask for an unbranded, BTU, U.K. model.