This is not a problem, we just need to reset it back to factory settings so you can start over in English. Follow the steps below. Please remember to rate my service before you leave today, and remember it is my service you are rating and not this website or your device. If for ANY reason you feel my service has been anything but excellent, please let me know before rating :)
1. Start with the phone turned off.
2. Now, hold the Volume up, Bixby and Power buttons at the same time.
3. Keep all three buttons held down until you see the Samsung logo.
4. Wait about 30 seconds and you should be taken to the 'Android Recovery Menu'. If your phone starts up as normal, you'll need to go back to step one and try again.
5. Press the Volume down button four times to highlight the wipe data/factory reset option.
6. Use the Power button to select it.
7. Now press the the Volume down button seven times until Yes - delete all user data is highlighted.
8. Use the Power button to start the wipe.
9. Wait a minute while the reset is carried out.
10. Once it has finished, press the Power button to select reboot system now.
11. Your Galaxy S8 will now begin to load up in its factory-reset state. It will take a few minutes for this first startup to go through, so you may need to wait a while before the setup screen appears.