Keyboard Layout indicator doesn't display current layout in Ubuntu 18.04 (empty drop down box)

A fix was released, already verified on Cosmic and Bionic.

EnableProposed

Until is added to normal repos, to enable them on Bionic (18.04) as said here, follow these instructions to enable the proposed archive, which basically say:

1. Enable pre-release updates:

2. Add to /etc/apt/preferences.d/proposed-updates

   Package: *
   Pin: release a=bionic-proposed
   Pin-Priority: 400
   

   If sudo apt-get upgrade -s return any package, something went wrong.

3. Run sudo aptitude -t bionic-proposed
4. Update with u
5. Select the proposed related packages:
   • gnome-shell-common 3.28.3+git20190124-0ubuntu18.04.1
   • gnome-shell 3.28.3+git20190124-0ubuntu18.04.1
6. Upgrade with g
7. Restart GNOME.

Please test it and eventually suggest changes to this post. If everything went OK upvote and share your love with the developers.

After some January updates got the same problem, but on Ubuntu 18.10. Reinstalling appindicator packages (see commands below), somehow partially fixed the problem: lang indicator stop disappearing in gnome-shell, but still do in gdm.

apt install --reinstall gir1.2-appindicator3-0.1
apt install --reinstall gnome-shell-extension-appindicator

Update 2019-01-20

the commands above didn't work. worked solution, at least for ubuntu 18.10 (Cosmic), is rollback to previous version of gnome-shell and gnome-shell-common packages:

sudo apt install --reinstall gnome-shell=3.30.1-2ubuntu1 gnome-shell-common=3.30.1-2ubuntu1

and perform the reboot

optionally, but highly recommend - prevent update on those packages, like these:

sudo apt-mark hold gnome-shell gnome-shell-common

and wait for fix. after fix will be released - just unhold those packages and run update\upgrade command.

for ubuntu 18.04 (Bionic)

you should try rollback those packages to 3.28.1-0ubuntu2 version.

possible origin of the problem

the only difference between old version and version at January update is in this bugfix; he also relate to ibus, so that fix may be the cause of the "disappearing lang indicator" problem