@Sergio23 , based on my test, I can run the exe successfully in the final. Therefore, I recommend that you check the following steps if the same as you or not.
First, Please check if your en-us folder has the Example.resources.dll and fr-FR folder has the Example.resources.dll.
Second, Please ensure that your en-us folder and fr-FR folder is in the same directory as the resources files and the txt files.
Third, We need to create the Example.cs manually(We could create a Example.txt file then change the extension to .cs) and copy all the code from the doc to Example.cs.(Example.cs is also in the same directory with resource files)
Finally, Please check if you used the following command to generate a exe.
csc Example.cs /resource:ExampleResources.resources