how to get icon in KDE systray

Do you run BIT as root? In this case this could be caused by xhost preventing root to draw on your desktop session.

You could test this with 'xhost +' (be careful as this will give everyone, even remote users, access to your desktop)

Thanks for your answer.
No, I run BackInTime as normal user.

Does it show up if you run a manual snapshot? If not please run 'backintime --backup' from command-line and post the output.

If it shows up with manual snapshot please run 'env -i HOME=$HOME USER=$USER backintime --backup-job' and post the output.

No, it does not show up when I run manual snapshot.
"backintime --backup" output is :
----------------------------
WARNING: import keyring failed

Back In Time
Version: 1.0.36

Back In Time comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to redistribute it
under certain conditions; type `backintime --license' for details.

INFO: Lock
INFO: on process begins
INFO: Profile_id: 1
INFO: Command "find "/media/denis/My Passport/backintime/backintime/denis-portable/denis/1/new_snapshot" -type d -exec chmod u+wx {} +" returns 0
INFO: Command "rm -rf "/media/denis/My Passport/backintime/backintime/denis-portable/denis/1/new_snapshot"" returns 0
INFO: Call rsync to take the snapshot

------------------------

I just double checked with a fresh install of Debian Jessie with KDE 4.14.2 but the systray icon was shown correctly.

Please post the output of the following commands:
ps ax | grep ksmserver
ksmserver --version
python /usr/share/backintime/kde4/kde4systrayicon.py

denis@denis-portable:~$ ps ax|grep ksmserver
 9720 ? S 0:00 kwrapper4 ksmserver
 9721 ? Sl 0:00 kdeinit4: ksmserver [kdeinit]
12109 pts/0 S+ 0:00 grep ksmserver

----------------------------
denis@denis-portable:~$ ksmserver --version
Qt : 4.8.6
Plate-forme de développement de KDE : 4.14.2
Le gestionnaire de sessions de KDE : 0.4

---------------------------
denis@denis-portable:~$ python /usr/share/backintime/kde4/kde4systrayicon.py
WARNING: import keyring failed
"KConfigIni: In file /home/denis/.kde/share/icons/MakLionTaste/index.theme, line 29: " Invalid entry (missing '=')
INFO: [kde4systrayicon] begin loop
------------------

That last command made the backintime icon appear in systray.

Okay, I see. Problem is your locale. Translators added a whitespace between KDE and the colon ( : )

Please use this patch with 'sudo patch /usr/share/backintime/plugins/kde4plugin.py < kde4plugin.diff'

http://pastebin.ubuntu.com/9321760/

Which locale do you use? We should report this as a bug against kde-workspace-bin

I applied the patch and checked it had been applied.
Then started backintime-kde and launched a manual backup.
But, unfortunately, the problem was not solved, still no tray icon.
My locale is fr_FR.UTF-8

Great, now it works !

Thanks Germar, that solved my question.