Geralt still speaks in his gruff English (or Polish) voice. The developers did not commission an Arabic dub due to the sheer volume of dialogue—over 450,000 words. Dubbing that into Arabic would have required months of studio time and a large cast of Levantine or Egyptian voice actors.
"The subtitles are mixed—some are Arabic, some are English." Fix: This usually happens if you updated the game mid-playthrough. Start a new game or verify your game files. Mixed languages are a known bug fixed by Patch 1.64. The Witcher 3 Arabic Language Pack Ps4
"The pack downloaded, but everything is still English." Fix: You changed the Game language, not the System language. Go to PS4 Settings > Language > System Language and select Arabic. The Witcher 3 does not have an in-game language selector for Arabic. Geralt still speaks in his gruff English (or Polish) voice