Well a German friend of mine who have the game found a solution, sort of.
In the game's folder nammed "Pack", if you rename the file "env_flotsamJungleNightClearing.dlg" into something else (I used env_flotsamJungleNightClearing_.dlg) then everything is working again.
When I went back to the portal, a cutscene started and I was able to finish the game.
He said that this trick is also working for the Chapter 4.
Hope it'll help people who are playing in german and french!
Thanks anyway for your help!