I wonder if anyone has problems running a Pharo on a 64-bit System
(Debian) with multiarch. Because strange enough it can suddenly not find
vm-display-X11 any more

You need to install the desktop variant:

$ apt-cache search pharo

pharo-vm-core - Clean and innovative Smalltalk-inspired environment.

pharo-vm-desktop - Clean and innovative Smalltalk-inspired environment.

pharo-launcher - Launcher for Pharo distributions.

So install pharo-vm-desktop and you�ll see

$  dpkg -L pharo-vm-desktop:i386 | grep X11

/usr/lib/pharo-vm/vm-display-X11.so

Hope this helps,

norbert