I frequently use the compose key to type special characters. I now have a fresh install of Ubuntu 14.04, and in the keyboard settings it says "compose key: disabled". I can't find how to set the compose key.
You will need to install dconf Editor from the Ubuntu Software Centre so it will appear in your applications.
If you use an applications list it appears under Sundry or if not in your Activities Overview (type dconf in the ~type to search~ box).
There are other ways of achieving your aim but this is a simple gui method not needing terminal skills.
$ dconf write /org/gnome/desktop/input-sources/xkb-options "['compose:{key}']"
where {key} is your chosen key-name (e.g. "['compose:ralt']" would make right alt your compose key.
