Thanks a lot for all your hints. The problem seems to be in the assembly System.Windows.Forms.dll, which is needed for ResXResourceWriter, but cannot be used in a console application. (Even in .NET, not just in .NET Core.)

Even when I tried to add the dll reference to my project, I got the Warning_MSB3290: Failed to create the wrapper assembly for type library ... Type library 'System_Windows_Forms' was exported from a CLR assembly and cannot be re-imported as a CLR assembly.

I eventually found the solution here. I installed the NuGet Package ResXResourceReader.NetStandard and that did the trick. So big thanks to farlee2121, even if he did not write any answer here. ;)