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The above link's solution worked for me.
I finally came to this bug report: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1372609
It seems FocalTech touchpad needs a specific driver, and that work is in progress to integrate it into the mainline kernel.
currently, there seem to be a ppa to get a dkms driver for this touchpad : http://ppa.launchpad.net/hanipouspilot/focaltech-dkms
After trying this, I can confirm the following procedure works :
sudo add-apt-repository ppa:hanipouspilot/focaltech-dkms
update the packages database
sudo apt-get update
install the dkms driver
sudo apt-get install focaltech-dkms
The touchpad in now recognized. Two finger scrolling works, for example. Also, the zone where the buttons are won't make the cursor move.
Thanks for the community that retro-engineered this (Asus just replied "no linux support nor technical information" to a request ! Very bad point to them (see the aforementioned bug report)).
Credit goes to alci and heemayl