Comment 54 for bug 548631

I used the following instructions given from a Romanian gentleman and it worked. Source: http://askubuntu.com/a/113517

As the best previous answer appears to be commented afterwards by the user as not working anymore, I will give here an updated perfected version of a quite successful workaround. Sorry not to be able to provide a more scientific less empirical approach, I am not an advanced user, just had the luck to get what I want in this case and want to share this, maybe as a temporary patchwork. So, bare with me. I use Xubuntu, maybe some instructions are limited to that.

My solution is this (my case is English-US as default, second French, third Romanian standard - replace accordingly):

Go to Setting Manager - Keyboard - Layout, and set the languages in the preferred order (delete them and add them in order to achieve this). Go to the properties of the xkb plugin and make the same settings in the same order with the same default language.

Open the file /home/username/.config/xfce4/xfconf/xfce-perchannel-xml/keyboard-layout.xml
Edit it to look similar to this:

<?xml version="1.0" encoding="UTF-8"?>

<channel name="keyboard-layout" version="1.0">
  <property name="Default" type="empty">
    <property name="XkbDisable" type="bool" value="false"/>
    <property name="XkbLayout" type="string" value="us,fr,ro"/>
    <property name="XkbVariant" type="string" value=",,std"/>
  </property>
</channel>

Open the file /home/username/.config/xfce4/panel/xkb-plugin-##.rc
Edit it to look similar to this:

display_type=1
group_policy=0
default_group=0
never_modify_config=false
model=pc105
layouts=us,fr,ro
variants=,,std
toggle_option=grp:alt_shift_toggle
compose_key_position=

Open the file (as root) /etc/default/keyboard
Edit it accordingly:

XKBMODEL="pc105"
XKBLAYOUT="us,fr,ro"
XKBVARIANT=",,std"
XKBOPTIONS="grp:alt_shift_toggle"

Maybe not all these are necessary to make it work, but just in case...