For Ubuntu 12.04 x86_64, the following worked:
1. Check en_US.UTF-8/Compose
2. Add export GTK_IM_MODULE="xim" to /etc/environment for a global change or create a ~/.gnomerc with that line for a single user's change
3. restart X
Solution found in http://wiki.ubuntuusers.de/Sonderzeichen
For Ubuntu 12.04 x86_64, the following worked: wiki.ubuntuuser s.de/Sonderzeic hen
1. Check en_US.UTF-8/Compose
2. Add export GTK_IM_MODULE="xim" to /etc/environment for a global change or create a ~/.gnomerc with that line for a single user's change
3. restart X
Solution found in http://