I am unable to install the game...towards the end of the installation process the installer throws this message;

There was a problem opening the file /home/hannes/Games/gog_s…gdom_simulator_2.0.0.2.sh.

The file you opened has some invalid characters. If you continue editing this file you could corrupt this document.
You can also choose another character encoding and try again.

I can pick three options:

auto detect
current locale (UTf-8)
Western (ISO-8859-15)

none of them work.

Did anyone here solve that problem?

I had the same problem with DLCs on a different game (Surviving Mars) when installing in Linux. Then I realized "Doah!" I forgot to make the file permissions "executable". Funny, that works.

What you're seeing (I think) is the message that a text editor throws off when you try to open instead of "run" said file (it takes a while to load/open and might have a status bar). So try working with the permissions or if your in windows just using the GOG galaxy installation manager.

Hope that helps.