How do you change language from english to french in the uk?

@BubbleBliss464  The U.K. version of Sims 4 is language-locked, so there's supposed to be no way to make it run in another language.  The Sims 4 user data folder in Documents\Electronic Arts is spawned as soon as you launch the game, even if it crashes right away.  So the presence of a "Les Sims 4" folder just means Origin tried to launch it in French, not that any French-language files were downloaded.

What you can try to do is repair the game in Origin, and if that doesn't help, change Origin's language to French, clear its cache, and repair again.

https://help.ea.com/en-us/help/faq/clear-cache-to-fix-problems-with-your-games/

However, I don't think this is going to make a difference.  Your copy of Sims 4 may well be hard-blocked from downloading any other language strings, in which case all you can do is change the registry string back to en_US and hope the game works again.