how to enable compose key in cinnamon?

I'm running Ubuntu 16.10 with Cinnamon, and I'd really like to be able to type diacritics. I saw this post:

How can I type accentuated characters like ë?

But I can't seem to set a "compose" key. I go into Settings->Keyboard->Layout->Options.

I expand "Position of Compose Key", and choose "Right Alt".

But...nothing happens. If I go into LibreOffice and type:

RightAlt: nothing happens Shift-Quote: I get a double-quote e: I get a lowercase letter "e"

But what I want is the "e" with the umlaut (?) above it.

Run the keyboard application (from menu or from the settings).

Choose the Layouts tab.

At the right bottom of the window, you've a Options... button.

You've then access to different options, including "Keyboard Layout Options".

I don't know anything about Cinnamon, but a generic way to designate Right Alt as a compose key is to edit /etc/default/keyboard and change the line:

XKBOPTIONS=""

to:

XKBOPTIONS="compose:ralt"

Another way to do what you want is to use a keyboard layout with dead keys. With e.g. English (US, international with dead keys) you can type ë by pressing Shift+' and then pressing E. (I'm guessing that you have a US physical keyboard.)

1. Menu
2. Preferences » System Settings
3. Keyboard (under Hardware)
4. Layouts tab
5. Options... (bottom right)
6. Expand Position of Compose Key
7. Check Right Alt (or other key if you prefer)