Having a two language website

Convert your site to a multisite, then …

  1. Create a second site. Set the site language to Persian in Options/General.
  2. Set the language of the first site to English.
  3. You can install a plugin to link translated posts like MultilingualPress (disclosure: I was the lead developer for that plugin for a long time).
  4. You can customize the Persian site now to handle RTL content better, for example with a dedicated child theme of the main theme and special plugins.

The post editor will now work automatically without further customization.