Most people's exposure to umlauts in English is limited to the affected, so-called "heavy metal umlaut" in band names like Motörhead, Mötley Crüe, Spin̈al Tap, etc.

What is not commonly known, except by those who've seen old books in print, is that the umlaut was used in written English as recently as the early twentieth century. It was used when a vowel appeared twice in a row within a word but spanned two syllables. Examples would be "preëminent" and "coöperate."

I think it's time to bring back the umlaut.