For German these rules are offical. They're used in the machine readable part of ID cards and passports. If you start at a german company and they setup an e-mail address for you they'll use these rules too. The origin of the letters ä, ö and ü in German are ae, oe and ue, people just put the e on top of the vowel and they slowly transformed into what we use today. You can still see this in some names like Goethe.