Hello and welcome
To use "custom application" in KangV Settings - if your language isn't English but German:
Open native settings, Advanced Settings, Language and Input and add to German English/German. Then change for a while the language to English.
Soon as your language interface is English you can choose any "Custom Application" in K-Settings.
It's only a language conflict. After you set up your Application you can change language back to German.
Thank you for your praise for my Rom.
At the moment I have several Huawei devices.
Mate 10 Pro, Mate 9, Honor View 10 and P9.
I am not sure yet which device I will use for my daily driver.
But I will make for all those devices (including P9 and P8) new ROMs.
My first Oreo Test Rom (including KangV Settings) I did for a friend of mine for Mate 10 Lite - everything perfect.
So I am ready in the knowledge how to do for Oreo.
I will even share the Mate 10 Lite Rom after my vacation here on xda.
And I am working on a solution for bringing Oreo to the P9 (if it will not come official)
In the meantime I have configured the classical hwota for P9 (which doesn't exist yet) for easily rebrand to other versions.
More to see after my "holidays" Thanks.