title_body: Adding a language that Calibre does not recognize
upvoted_answer: Farsi
  
  Speakers of Persian (and related languages) usually use Farsi in their native languages to refer to Persian in the same way a French speaker would use Français to refer to French. However, no French speaker would ask a software developer to use Français also in English GUIs.
  
  If you want to have Farsi as a menu option, you'll need to change the UI language to Persian or a related language.
  
  Hindavi 
  
  Since Calibre uses ISO language codes internally and there are no ISO codes for Hindavi/Hindustani, it's not possible to add a Hindavi menu option. You'll have to use Hindi.