Re: EA app changed language of The Sims 4?
It is also possible to change the language by editing the registry.
In my case, first changing key "Locale" in
"HKEY_LOCAL_MACHINE\SOFTWARE\Maxis\The Sims 4"
and
"HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Maxis\The Sims 4"
to "cs_CZ" for Czech (you need to figure out the locale code for your language yourself),
then in EA App click The Sims 4 > Manage > Repair.
It will download the string files responsible for language and when done, the game will run in the desired language.
If you don't understand any part of this answer, the safest bet would be to just reinstall the game.