Hello, Mohammad.
Just change your Xbox country to United Arab Emirates from settings, uninstall the game and reinstall it and your problem should be solved. The Arabic subtitle and menu will be available in game's settings
I was able to find the formula in an unexpected place in Velen, it's in a half-broken ship inside a chest. Btw I would recommend saving first because you may encounter a glitch and get trapped underwater.
Here's is the PROOF & LOCATION.