Hey @elwinl from what I found Dutch is not supported from side of Alexa, so you would have to use english.
And it's true that the wibutler skill is only available in Germany as of now.
What you can try is, with your wibutler skill already activated, to go into the alexa app and go to
"More" -> "Settings" -> "Alexa App Settings" and change the language to "English -UK" there.
That should allow you to control your connected devices via alexa in english.
I know it is only a workaround but maybe it is working for you aswell, until we have activated the skill for additional countries.