Indeed, if you look at the session file in "~/.x2goclient/sessions" which contains all the configuration of the session of x2goclient application you will see all the descriptions of each session.
Which looks like this for each session:
[20150220100323537]
speed=2
pack=16m-jpeg
quality=3
fstunnel=true
export="/home/user/Bureau/MountDistantX2goPc:1;"
iconvto=UTF-8
iconvfrom=ISO8859-1
useiconv=false
fullscreen=false
multidisp=false
display=1
maxdim=false
rdpclient=rdesktop
directrdpsettings=
width=800
height=600
dpi=96
setdpi=true
xinerama=false
clipboard=both
usekbd=true
type=auto
sound=true
soundsystem=pulse
startsoundsystem=true
soundtunnel=true
defsndport=true
sndport=4713
print=true
name=username
icon=:icons/128x128/x2gosession.png
host=localhost
user=userTest
key=
rdpport=3389
sshport=2222
autologin=false
krblogin=false
krbdelegation=false
directrdp=false
rootless=false
published=false
applications=WWWBROWSER, MAILCLIENT, OFFICE, TERMINAL
command=SHADOW
rdpoptions=
rdpserver=
xdmcpserver=localhost
usesshproxy=true
sshproxytype=SSH
sshproxyuser=usernameProxy
sshproxykeyfile=
sshproxyhost=123.452.111.124
sshproxyport=22
sshproxysamepass=false
sshproxysameuser=false
sshproxyautologin=true
sshproxykrblogin=false
The part which interest me is the bold part.
Indeed, it works when i'm using this conf file with x2go client.
And when i'm using x2goplugin with this configuration it doesn't work. I take a look at the network traffic and it seems that x2goplugin doesn't look at the bold part (the ssh proxy).
This is why I think that x2goplugin doesn't work with ssh proxy.