Question

انها خیلی اهل تعارف هستن

 به انگلیسی 

Answer 1

They  stand on ceremony much

they  behave in a formal way too much/they're always [OR] constantly behaving formally

IDM= STAND ON CEREMONY=To behave formally

e.g:there is no need to stand on ceremony,come in and relax

please don't stand on ceremony with me

Answer 2

می تونید از همون واژه taarof استفاده کنید که در ویکی پدیا هم هست و در متون خارجی برای رسوندن نزدیکترین مفهوم استفاده میشه. 

They are much into 'taarof'. 

They do a lot of 'taarof'. 

https://en.wikipedia.org/wiki/Taarof 

http://www.latimes.com/local/great-reads/la-me-c1-tarof-20150706-story.html 

http://www.urbandictionary.com/define.php?term=Tarof 

 

Persian Mirrors: The Elusive Face of Iran

https://books.google.com/books?isbn=0743217799

Elaine Sciolino - 2001 - ‎History

My mother always tells me I have bad manners because I usually don't 

do taarof. But in this case, I felt I had no choice. No harm was done.