How do I disable emoji input in Ubuntu Mate 18.04?

Just a small hint: In case you don't find the IBus Preferences dialog, open a Terminal shell and type

ibus-setup

A dialog like this will appear on your screen:

Turned out it was the new ibus version that included the emoji package, I was able to change the shortcut in the ibus settings.

For VS Code if installed via Ubuntu Snap you need an input method other than ibus.

If you run VS Code from command line do:

$ GTK_IM_MODULE="xim" code

You can also add an alias for that in .bashrc: alias code='GTK_IM_MODULE="xim" code'

To configure the Dash launcher (assuming VS Code is installed using Snap):

• The launcher file is located at /var/lib/snapd/desktop/applications/code_code.desktop or ~/.local/share/applications/code_code.desktop, or both
• Edit it and add GTK_IM_MODULE="xim" to Exec commands:

[Desktop Entry]
...
Exec=env GTK_IM_MODULE="xim" BAMF_DESKTOP_FILE_HINT=/var/lib/snapd/desktop/applications/code_code.desktop /snap/bin/code --force-user-env --no-sandbox --unity-launch %F
...

[Desktop Action new-empty-window]
...
Exec=env GTK_IM_MODULE="xim" BAMF_DESKTOP_FILE_HINT=/var/lib/snapd/desktop/applications/code_code.desktop /snap/bin/code --force-user-env --no-sandbox --new-window %F
Icon=/snap/code/41/meta/gui/com.visualstudio.code.png