

Just use the regular letter instead of the Umlaut
But that’s just wrong. ü has a different meaning and pronunciation than u.
If umlauts aren’t available, the correct way to write umlauts is with an additional e: zurueck.
Über-Mensch -> Uber-Mensch
Please be aware that this term can be problematic, since it can be seen as a foundation for fascist ideas. https://en.wikipedia.org/wiki/Übermensch#Use_by_the_Nazis

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