For iPhone User please try "AEI Keyboard Note" App. (This app is Free)

Original German Keyboard for iPhone & iPad
* With Arrow Keys
* Ideal Key for iPhone
* Easy to input “ä Ä ö Ö ü Ü ß"
* iPad Special Ten Keys like PC Ten Keys.

Useful keyboard Settings (tap"tools")
You can turn off Key Sound from it.

Please add this Keyboard from iOS Setting and switch "Allow Full Access"

Note : This app may not work on Old Apps.