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Hey guys,
I had the same problem when I bought the game on release, really bummed me out. Based on what I looked up I figured out how to fix it. Hopefully this works for others as well:
1) Navigate to C:/Program Files (x86)/Origin Games/The Sims 4/Data/Client
2) Delete the file "Strings_ENG_US.package" entirely. For other language users this file will be similar in obvious ways.
3) Navigate to C:/Program Files (x86)/Origin Games/The Sims 4/Game/Bin
4) Delete the file "TS4.exe" (the application file with the logo on it)
5) Launch origin, right-click The Sims 4, and proceed to download it. Don't worry if it tells you it's gonna download the whole game, because when it begins it'll be on 99%. It's just gonna re-download those language files and the .exe.
6) Launch the game. Problem solved (hopefully).
P.S.: Don't reinstall your entire game unless you're prone to modding it and have thus done so. Stuff like this is usually a matter of a few files, and even Origin has a repair function that can redownload these files. Besides, if you are a keen modder you should probably either know all this already and keep a backup just in case.
Good luck!
Kind Regards,
Laura.