Setup process loops at "Choose a language"

[mherfurt]

First: Thanks for your effort in providing/maintaining so many containers!
Yesterday, I tried to deploy your invoiceplane container on my kubernetes environment. Everything works perfectly, but when the setup process starts, it won't get past the point where I have to choose an installation language. By manually typing the page-name "setup/prerequisites", I can see that all the required things are fulfilled. By clicking on "Continue", I end up with language selection again.
I know that this is primarily a software issue, but I would like you to know about.
Any help would be appreciated!