You may be region locked. When you set your location, you're only able to choose between the languages your country supports. So, for example, you'd only find German in Germany.
You'll need to go to your Xbox's settings via the home screen and then change your location to one that would support English (United States or Canada, for example). Then, you should be able to select English as an option.
Use the Offline System Update Diagnostic Tool on your Xbox One to troubleshoot your error. You'll need to use a flash drive that's converted to NTFS.
How to use the Offline System Update Diagnostic Tool on Xbox One
If going through this process doesn't work, you'll need to reset your Xbox to its default factory settings. Do this by hitting the "Restore Factory Defaults" in Step 2 of the Offline Diagnostic Tool.
If that doesn't work, you'll need to send in your console to be repaired.
You can delete games by selecting it and holding left option button (VIEW) (the one with two rectangles) and pressing A and "unistall".The manual is digital and you can access it directly on console by opening application with "?" as icon.
If your code is invalid, you need to contact QVC or Microsoft to reissue you a new code.
As for SMITE, if you've redeemed the code for SMITE (While I'm not sure why you would need to since the game is Free to Play) you can find it in the online store and doing a search on smite.
If you've registered your Xbox One, you alternatively go here: https://store.xbox.com/en-US/Xbox-One/Games/SMITE/9e606d9f-777c-4921-a038-81e87dc381c0
Then click download and download to your Xbox One the next time you turn it on.