translate only one word in php

Hi everyone!
I made an e-commerce using polylang, in two languages, italian and english, and added a filter to have one more field on the checkout page. Since I’m not sed to php, I just found that code that was useful for italian but how do I translate that single field in english using php? It doesn’t appear in the strings obviously, so I have no clue on how to do it. thank you.