Alright, I started all the trouble myself, but wasn’t aware of it!
What I did?
I created a separate app for Windows Phone 8, similar to Windows Phone 7 but a complete new code base. At that time I also did not have interest in making the Windows Phone 8 app multilingual. The Windows Phone 8 app only supported Dutch, instead of the three languages that were supported by the Windows Phone 7 app. The expected result I thought: Windows Phone 8 will only get the Dutch app, the Windows Phone 7 users are going to get the multilingual app.
The actual result
Testing was successful, but the Windows Phone 8 specific version doesn’t appear in the Store. I didn’t know what to do, so I asked my local Windows Phone champ, Rajen Kishna. He contacted the Windows Phone team, and came back with the cause and even a solutions.
As you can see in below screenshot the supported languages are different for the two versions of the app. The Windows Phone team explained that when the language selection isn’t equal the oldest version is served.
Make sure that the language selection is equal for both apps. Probably most of us would make sure that the Windows Phone 8 app would support German and English as well. I didn’t, but the main reason for this is the business model behind the app (I’m only earning money with the Dutch version).