You usually use "fiancé" with "é" and not "e" as "fiance". Why?
I know "É" is a letter of the Latin alphabet, and the word "fiancé" refers to mid 19th century: from French, past participle of fiancer ‘betroth’, from Old French fiance ‘a promise’, based on Latin fidere ‘to trust’.1
I know it is a loanword (like résumé from French) a word adopted from one language (the donor language) and incorporated into another language without translation.
But why don't you translate it into English? Why "é" remains original?
Best Answer
Asking "why" about any question of English spelling is a hopeless task.
In the 1800s some people decided to start using the French word for a person who was going to get married. We don't know why they did this — there was a perfectly good English word "betrothed" that they could have used instead. Perhaps they felt the English word sounded too plain, and the "romantic" French word was sophisticated.
When they wrote the word, they copied the French spelling with an accent on the e. Some other people wrote the word with no accent, and were told that they were "wrong". People get very opinionated about details of spelling. But enough people either didn't or couldn't write the word with an accent to make this spelling quite common.
The result is that two spellings are in common use.
The general observation is that when English people borrow a word from a language that uses the Latin alphabet, it is common for the spelling to preserve the accents in the source language. This is especially common when borrowing from Western European languages, whose diacritic and alphabet systems are most familiar. It is also more common when the accent indicates a significant difference in pronunciation. Usually, over time, the accent is lost. So older borrowings are less likely to use accents.
Here are some examples of borrowed words that can be correctly spelled in two ways