[thaumasiotes]

> English does not contain diacritics.

Tell it to the New Yorker, where orthography like coöperate is required by official policy.

As they would no doubt also be happy to explain, the diacritic there is not correctly referred to as an umlaut, as "umlaut" refers to the difference in pronunciation between e.g. German "u" and German "ü", while the diacritic in coöperate doesn't change the pronunciation of any letter but instead exists to indicate to the reader that the two letter Os are to be pronounced separately rather than interpreted as a digraph (as in "troop").

It is somewhat interesting to note that modern English speakers often feel that a mark for this purpose is needed, even though formally the orthography doesn't call for it - but they are much more likely to write "re-emerge" than to write "reëmerge".

[donatj]

One publications strange style guide does not a language make.

[thaumasiotes]

It's not difficult to find diacritics in use outside the New Yorker, though generally not in that use. One exception would be the common spelling "naïve".