The game won't launch due to the missing executable files which the developers kinda forgot to include as they stated themselves in August:

Dowser.exe problems, game not launching
We made a fix for people having the 'missing executable' issue, playing from: Latin America, Russia, CIS, Korea.

To resolve the issue, please:
1. Shut down and restart the steam client.
2. You should get an update.If not, please verify files.
That should fix the issue

Unfortunately, my country, Czech Republic is not in Latin America, Russia (although our president would love that), or CIS (former eastern soviet states).

This "solution" is laughable as it hasn't helped most people. There are many other "solutions" which haven't helped almost no one.

The problem looks like this:

You need to get the aforementioned executable files. You could probably get them from a friend if they have the game.

There is an easy solution you can do on your own.

• Download a Paradox Launcher and install your game there. It is linked to your Steam account, so you have all of your games published by Paradox there. You can play it there, but you probably want to do it on Steam.
  
• Copy the mentioned files from the Paradox Launcher game files to Steam game files.
  
• Enjoy the game.

On the left, you can see the game files from a Paradox Launcher. On the right Steam game files. Just in case, copy&paste it all.



I hope that this will help someone.