Option to enable extra keyboard layout is lost

Vasyĺ,

Do you mean the System Settings > Keyboard Layout dialog? If you click on the "+" button then you will get a choice of hundreds of layouts. Or do you mean something different?

Yes, that is the very dialog. And if I click on the "+" button then I'll really get a choice of hundreds of layouts, but without extra layouts I need! E.g.:
$ grep name\>ru\< -A20 /usr/share/X11/xkb/rules/base.extras.xml | grep -B2 description
        <name>ru</name>
        <shortDescription>ru</shortDescription>
        <description>Russian</description>
--
          <configItem>
            <name>chu</name>
            <description>Church Slavonic</description>
--
            <name>ruu</name>
            <shortDescription>ru</shortDescription>
            <description>Russian (with Ukrainian-Belorussian layout)</description>

As you can see there are no "Church Slavonic" and "Russian (with Ukrainian-Belorussian layout)" layouts in Keyboard Layout dialog, because they are placed in the "extra" section and the system doesn't read "extra" rules by default, moreover it hasn't an option to enable this feature.

Daniel,
Do you need some more explanations about the bug?

Could somebody change the bug status to something more definite?

[Expired for gnome-control-center (Ubuntu) because there has been no activity for 60 days.]

Let me try to explain in another way.

Issue:
The keyboard configuration module of the gnome-control-center is totally ignore keyboard layout rules which are placed in /usr/share/X11/xkb/rules/base.extras.xml.

Consequences:
All keyboard layouts from "extra" section of xkb-data are not available for use.

Solutions:
1. Make gnome-control-center to read rules from /usr/share/X11/xkb/rules/base.extras.xml by default.
   or
2. Create an option (Check Box) in gnome-control-center that enable extra keyboard layouts.

Thank you for taking the time to report this bug and helping to make Ubuntu better. The issue you are reporting is an upstream one and it would be nice if somebody having it could send the bug to the developers of the software by following the instructions at https://wiki.ubuntu.com/Bugs/Upstream/GNOME. If you have done so, please tell us the number of the upstream bug (or the link), so we can add a bugwatch that will inform us about its status. Thanks in advance.

Status changed to 'Confirmed' because the bug affects multiple users.

So upstream fixed the bug last year. But this fixing didn't resolve the Ubuntu issue.
Even after enabling extra sources:
$ gsettings set org.gnome.desktop.input-sources show-all-sources true
extra keyboard layouts are still not accessible from System Settings > Keyboard Layout dialog.

It still doesn't work for Ubuntu Trusty beta. Can anyone suggest at least a non-destructive walkaround?

The command line way to enable the extra layouts is:

gsettings set org.gnome.desktop.input-sources show-all-sources true

It would be nice if a "Show all sources" option - please see the attached image - could be added to unity-control-center. I'm not sure about the label, though. Maybe "Show extra sources" would be better.

I talked with Sebastien Bacher on IRC about the idea to add a GUI option:

https://irclogs.ubuntu.com/2017/01/20/%23ubuntu-desktop.html#t09:57

After that I have checked out what the official flavors do today, and found that Kubuntu shows the whole list by default, but not the other flavors. As far as I could see noone has a GUI option for the purpose.

There are pros and cons with a GUI option. However you label it, most people won't understand what it is about, which wouldn't be good from a design POV.

So let's consider this bug fixed given that we now have a gsettings option which can be changed either via terminal or via dconf-editor, and which is honored by both u-c-c and g-c-c.

As regards Ubuntu I have added a note to the desktop guide:

http://bazaar.launchpad.net/~ubuntu-core-doc/ubuntu-docs/trunk/revision/595#ubuntu-help/C/keyboard-layouts.page