I searched for .TTF in UE4 Folder for find the font of that section, I found that , Now you can replace every Persian or Arabic fonts in this folder:
UE 4.xx\Engine\Content\Slate\Fonts
1.create a copy of from your font and paste beside itself (you have two fonts )
2.rename two your fonts to: DroidSansFallback.ttf and DroidSansMono.ttf
Note: Both fonts must be a font
3.Replace the your fonts to: 4.xx\Engine\Content\Slate\Fonts
you can download 3 Sample font from google drive: [Persian Font for UE4][4]