Can you think of an English word, not borrowed from another language, that has an accent or other diacritic? (a diacritic is simply any glyph added to a letter: see here for examples).
You may not be able to think of many, because English of course doesn’t really use any diacritic marks. You might be able to think of some words borrowed from other languages that retain them. Exposé for example, or façade. They’re useful in those cases to indicate pronunciation, particularly for exposé, to distinguish it from expose. Generally though, when importing words from other languages, we don’t tend to keep the diacritic marks. It used to be more common. Even into the early 20th century, it was fairly common to spell the words hotel and role with a circumflex over the O, as in French, like so: hôtel and rôle. Nowadays though, we tend to avoid diacritics entirely.
With one exception though, as there is one diacritic mark which is officially used in native English words. You may have figured it out if you thought of names like Zoë, Chloë, or Noël. This mark is best known by its German name umlaut, though in English it’s known as a diaeresis. It’s function can be easily figured out from the examples above: it indicates that the second vowel is pronounced separately from the preceding vowel, and is particularly useful when those two vowels together normally produce a particular sound.
You might think that proper nouns don’t count, particularly because the ones I mentioned above are also used in other languages. That’s a fair point, but it’s also possible to use a diaeresis in other English words. This article, for example, which inspired this post, features such a use. Notice how the author spells coöperate, beginning in the third paragraph. I was initially taken aback when I first saw it, as I’m not used to seeing it spelled with a diaeresis. Most people use a hyphen to separate the prefix and the rest of the word, or don’t bother doing anything at all (cooperate, which I hate). The diaeresis makes sense in this case, as it does in other words such as daïs and reëlect.
It’s never really necessary to use a diaeresis, but at least now you have an answer to a possible quiz question, and you can add a little flair to your writing!