Awesome, I figured it out. Run this command, which rebuilds LaunchServices:
/System/Library/Frameworks/CoreServices.framework/Frameworks/LaunchServices.framework/Support/lsregister -kill -r -domain local -domain system -domain user
And everything should be back to good! Immediately after running, the App Store allowed me to re-purchase the app.
Source: MacLife Link
Google and Spotify are most likely showing you Netherlands information because they are associating your IP address to a location in the Netherlands.
This isn't a setting that is controlled from your browser, but is a component of your internet connection that services use for various reasons to personalize the experience to the user, without knowing much (yet) about the user themselves.
For example, if I VPN (tunnel my internet connection to make it look like I'm from a server physically located elsewhere) from the US to the UK, Google automatically directs me to the UK Google page, and I can watch Al Jazerra English and BBC. (both unavailable-ish in the US) Similarly, those services think you are physically in the Netherlands, and they behave accordingly; Google directs you to it's .nl service, and Spotify likely doesn't have streaming agreements in the country, so it cannot legally service those in the Netherlands.
Now, you don't mention where you are physically, so it is possible that you are not physically in the Netherlands, but whatever service Google and Spotify use to associate an IP with a general location says that you are, likely because (some time in the past) that IP address was associated with a location in the Netherlands. If that's the case ... you may need to contact your ISP to see if they have a remedy for this kind of problem.
Best Answer
One way to do this is to go into the app (control click, show package contents, contents, resources) and switch the names of the .lproj files, so that the one corresponding to your OS language actually contains the data for the language you want the app to display in.
This will only work if the application in question is properly localized for the locale you choose. Also, be sure you have a backup copy or plan to reinstall the app in case modifying it breaks anything.