If you don’t want to write the umlauts (, , ) in fully spelt way, you can use a simple trick to produce with, for example, American keyboards by pressing a certain combination of keys, called ASCII Codes. So make this work, you have to use the numbers at the right of your keyboard and press "Alt" all the time while typing in the numbers. (In brackets you'll find the way they are spelt if nothing's working, everyone will understand what you mean then)

Alt + 132 = (ae)
Alt + 142 = (Ae)
Alt + 148 = (oe)
Alt + 153 = (Oe)
Alt + 129 = (ue)
Alt + 154 = (Ue)

Alt + 225 = (ss)