OK, thank you for the explanation (and thanks to @dtgreene too). For the script, i don't really know... Goes to /proc directory and displays the kmem file before exiting ?
eiii: dash is a rather minimal implementation of a bourne shell (sh) and is smaller and faster than bash. That's why it has replaced bash as the default system shell on some distributions. But bash understands more commands. And when the script in an installer uses one of the commands which only bash understands, but wrongly declares /bin/sh instead of /bin/bash for execution, it will fail.
But here's the important thing : i've finally managed to install the game, using a weird trick. As said, i have a few installer files because i have downloaded it several times. Each installer has its own crash time. I began the install with one, and when it crashed, i made a copy of every single file installed so when the crashing installer erased them, i could put them back in their directory. Then i run the second installer and told him to never overwrite files. So it installed the files coming after the files installed. Then it crashed, so copy/paste, then run the 1st intaller until it crashes, rinse and repeat until the game's fully installed. And it works !! Had a lot of crashes at the beginning, but setting down the graphics options seemed to make it good.
But it might be the longer install i ever done !