how to change the language of the game?

silverchariots2​  Try playing in a clean user folder, just to see whether there's any residual content in the old folder that's getting in the way.  Move or rename the Sims 4 folder in Documents > Electronic Arts, and when you open the game, a clean folder will spawn with no content.  Start a new save and have a look around.  If everything is fine, you can move your old saves and anything else you want to keep to the new folder.  Keep in mind that the sims' names won't change when you change the language.

If the game is still in English in a new folder, you'll need to uninstall and reinstall the game.  I'd suggest a clean uninstall since the repair process didn't work, and it's not much slower than a regular one.  Here's how to do it:

📓[GUIDE] [PC] How to Clean-uninstall Sims 4 | EA Forums - 12636503

it's the latter. i tried to repair the game a couple of times and nothing happened. i tried to change to another language and it still didn't work.

silverchariots2​  Are you saying that you choose a different language in the EA App, under Sims 4 > Manage > View properties, and that the language the EA App shows reverts?  Or does the language you choose in the EA App stick, but the language in the game doesn't change?  If the latter, please post screenshots of examples of the language not being the one you chose.