This is the answer that AirbnbHelp Twitter account gave me (My receipt is in Turkish even though I changed the language of my account into English):
"If the preferred language of your Airbnb account was Turkish when the receipt was generated and sent out, then your receipt will appear in Turkish. If you changed your preferred language to English after your receipt was sent to you, we would not be able to change the language on your receipt to send a new English receipt. As your preferred language is now English, all future receipts will be sent to you in English. We're truly sorry for any inconvenience."
It is extremely annoying that they are not helpful at all.