The best replacement for umlaut is diaeresis.

The best alternatives to umlaut are rated as following:
★★★★★  diaeresis
★★★  cedilla
★★  ablaut
★  tilde
★  trema
★  dieresis

Your alternative for umlaut is not listed? Suggest!
Speaking about umlaut, one probably shouldn't forget about u.

Other search terms related to umlaut and their ratings are:
★★★★★ u
★★★ o
★ a
dash
e
You have in mind a companion for umlaut and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of umlaut in all years. Click on graph for more.
umlaut
diaeresis
cedilla