Comment 1 for bug 1635090

We can enable typing of additional typographic symbols by adding 'misc:typo' value on 'org.gnome.desktop.input-sources xkb-options' path via gsettings or dconf-editor. Also we need to add key for choose 3rd level (for example Right Alt - 'lv3:ralt_switch'). As a result, the keyboard layout would look like this: https://launchpadlibrarian.net/266996930/Russian_keyboard_layout.png

This method works fine for me on Russian and English keyboard layouts, but there can be problems with layouts with native 3rd level (such as German or Spanish). For this reason, this option was not included in switchboard-keyboard-plug. OP, you can ask @santileortiz in Slack for more info.

I am sure this option is necessary, but we need ideas how to implement it.