How to run the game on Linux? After unpacking the package with the game (gog_the_witcher_2_assassins_of_kings_1.0.0.4.tar.gz 21,2Gb) I have the following files and directories: docs, game, support, start.sh.

./start.sh: 6: ./start.sh: declare: not found
./start.sh: 7: ./start.sh: declare: not found
./start.sh: 8: ./start.sh: declare: not found
./start.sh: 9: ./start.sh: declare: not found
./start.sh: 12: ./start.sh: Bad substitution
./start.sh: 12: ./start.sh: declare: not found
./start.sh: 18: ./start.sh: source: not found
./start.sh: 41: ./start.sh: define_option: not found
./start.sh: 44: ./start.sh: standard_options: not found

Running files from the directory / game does nothing.
/game/configurator has no effect.
/game/desktop-launcher starts the boot menu and nothing else.
/game/launcher launches the start menu and nothing else.
/game/witcher2 has no effect.

My system is:
Ubuntu 14.10 64bit
12GB ram
MSI GF 460GTX764ram

edit---
OK, the command ./start.sh activate the start menu, but the terminal returns:
Running The Witcher 2 Assassins Of Kings
Gtk-Message: Failed to load module "overlay-scrollbar"
Gtk-Message: Failed to load module "unity-gtk-module"
Gtk-Message: Failed to load module "canberra-gtk-module"
** Message: window size should be 487x713
./witcher2: error while loading shared libraries: libSDL2-2.0.so.0: cannot open shared object file: No such file or directory

Try this:
sudo apt-get install libsdl2-image-2.0-0:i386 libsdl2-ttf-2.0-0:i386 libcurl3:i386

But the game crash me right after startup.