Compose key not working on Ubuntu 16.04

I was having a very similar issue and for some reason what worked for me was putting all my custom compose key settings at the top of the original file all the way over in /usr/share/X11/locale/en_US.UTF-8/Compose and then making a hardlink to it called .XCompose in the home directory instead of writing my own .XCompose in the home directory from scratch. It worked for me, maybe it'll work for you.

I had a similar problem with the Compose Key upgrading from 14.04.3 to 16.04 (US-keyboard used also for german, french and italian). My choice for the compose key was the RightAlt key (al least for the last 10 years). After many unsuccessful trials and after searching everyhere for help I understood that I was fallen victim of the bug #1573755 and gave up, temporarily using an old 14.04.

But all my troubles under 16.04 disappeared abruptly last weekend after I configured the Compose Key as Shift-RightAlt. All my applications from vi to emacs to LibreOffice are now working perfectly. No other configuration gave me the same result. I do not know why, but hope that it can help. Regards Franco

I had the same problem and solved it with these steps:

1. Remove (or comment) any lines that deal with XIM configurations from your ~/.profile:

   # export GTK_IM_MODULE="xim"
   # export QT_IM_MODULE="xim"
   # export XMODIFIERS="@im=none"
   

2. Set the input method "XIM" from the Language Support tool instead:

   

3. Remove (or move) your ~/.config/dconf/user file (here's some info on what dconf is).

4. Log out and log in again.

Thanks to Gunnar Hjalmarsson for pointing the bug #1573755 out. If this solutions doesn't work for you, you might find something useful in the thread.

Adding ibus-daemon --xim as a startup application fixes this for me. None of the other suggestions here worked.

Steps for doing this are:

• Search for 'startup' using the Ubuntu search button on the toolbar (also accessible via the windows key). Select Startup Applications
• Click the add button. In the dialogue that follows enter the following information:
• Name = Ibus Daemon (or whatever)
• Command = ibus-daemon --xim
• Comment = whatever you like
• Click Save
• Log out and then back in.

I had the same problem after upgrade from 20.10 to 21.04. In my case the problem was with invalid LC_TIME environment variable setting, after I set LC_TIME to correct value my XCompose started to work again in firefox and geany.