As I understand, ö in coöperation is considered archaic (or is it?) and words like résumé, cliché and naïve are copied directly from foreign languages.
Are there any contemporary native (non-borrowed) English words left that contain characters with diacritics?
Update: Note that a word from any contemporary dialect of English would work for this question.
Also, of course, as is noted in answers below, besides borrowed foreign language words, there are English words with diacritics, that were created from non-English given names — like ångström for example.
Such words, arguably, also can be considered borrowed. And, at least with ångström, Wikipedia claims that version with diacritics is archaic as well.
Update 2: To clarify:
Contemporary = was a norm in XX century at least (preferably after twenties as well). When I said "archaic" in comments, I meant "non-contemporary".
Diacritics, which appeared in anglicization of a borrowed word (i.e. foreign original does not have diacritics), is acceptable. (So, Brontë surname would be good if survived into XX century.)
(Anyway, is there a source where I can read about the rules which guide when diacritics should appear during "contemporary" anglicization?)
I'm not sure if proper nouns are in the spirit of the question — but if you know one that fits and is not synthetic (i.e. employs "metal umlauts" or imitates some foreign language), please share.