This term may seem like it's French, and it is, but it's actually quite commonly used in Persian as well! Merci is written as مرسی in the Persian alphabet. While it's not originally Persian and you may be confused on why you'd use French, the word is quite useful, especially in Iran.
How do you reply to thank you in Farsi?
https://www.youtube.com/watch?v=ZZcWmqE2dRg
What is Merci in Persian?
Mersi (مرسی) or Merci You can use the French loan word, Merci – pronounced “mer-see” with a rolled r. It is an informal term which is used commonly within Farsi-speaking communities. As a response, you may hear khahesh mikonam (خواهش میکنم) meaning “you're welcome”.