Play the sims 4 in another language

@Tikkizen  It sounds like you might have the language-locked English-only version of Sims 4 on your account in addition to the global version.  You have two options here.  One is to contact EA customer support and ask that the English-only version of the base game be removed from your account.  Make sure support also checks for and removes, if necessary, the Digital Deluxe upgrade.

https://help.ea.com/en/contact-us/

It would be best to use the live chat option rather than email.  If you don't see it, set the location in the lower-right corner of the browser window to U.S. or U.K., or choose a slightly different category of issue.  Sims 3 > PC > Manage my account > Find missing game should work, with the live chat option below the email form.

The other option would be to install through Steam, which only offers the global version of Sims 4.  If you've already installed through the EA App, uninstall that copy first.  After you downloaded the game, you'd sign into the EA App and install your owned packs, but NOT a second copy of the base game, and all those packs should load when you're playing through Steam.