What are the criteria to adopt new words into English?
There are many words or phrases in English that are clearly of foreign origin yet become so commonplace they are indiscernible from the rest of English and make their way into English dictionaries.
Examples include deja vu, carpe diem, kosher and rendezvous.
However, there are plenty of foreign-language phrases, such as c'est la vie and hasta la vista that are used in English and will probably not appear in an English dictionary or be considered English.
So, how and when does a foreign word or phrase become adopted as English and how and when does it remain foreign?