Ok. If you go to your editor settings you can change your language to be Arabic specific. You’ll find it under the Appearance section in your build, I believe.
Next you need to go to UE4\Engine\Config\Localization and open up the Editor.ini and Engine.ini. In there you’ll find a CulturesToGenerate array, you should add Arabic to both of these.You should consider removing the other language so as to not corrupt your content and iterate faster.