It has nothing to do with a German umlaut. It is a diaeresis, and its use in English is perfectly valid (if uncommon). https://en.wikipedia.org/wiki/Diaeresis_

It has nothing to do with a German umlaut. It is a diaeresis, and its use in English is perfectly valid (if uncommon). https://en.wikipedia.org/wiki/Diaeresis_(diacritic)#English https://en.wikipedia.org/wiki/Diaeresis_(diacritic)#English