Hi,there are four variants of the name:
Gillenbach
Gielenbach
Gilenbach
Güllenbach

That is indeed quite odd, I found official documents going back and forth between the names. It seems noone can quite agree on what it is called officially.
For example gillenbach is used here: https://www.ravensburg.de/rv-wAssets/pdf/wirtschaft-planen-bauen/bauleitplanverfahren/Laufende-Bebauungsplanverfahren/Brachwiese-III-Neuaufstellung/Brachwiese-III-Neuaufstellung.pdf
and then güllenbach here:
https://www.ravensburg.de/rv-wAssets/pdf/wirtschaft-planen-bauen/T27-1_BPlan-Lageplan.pdf

I will implement your suggestion and ask the city of ravensburg if they can clarify.

Greetings,
WWM