unity - missing indicator-datetime in Ubuntu 14.04.2

[Running Ubuntu Desktop 14.04.2 x86_64 -- 3.16.0-41-generic -- on an Intel DuoCore T9300]

My Unity bar indicator-datetime disappeared suddenly about a week ago. No warning and no other problem apart from 2 days later the disappearance of indicator-stickynotes too.

Those two events only affect my account-session on my workstation. Other users on the same machine, using the same hardaware, are fine on both counts (indicator-stickynotes and indicator-datetime).

I am in the process of filing a specific bug for `indicator-stickynotes, although the coincidence is too much of a red-flag not to raise broader questions about the unity environment itself or perhaps before that, just about my user profile... In reality I am in the dark.

Interestingly indicator-datetime still shows in the Unity bar on the session login screen. After login it is gone. All system-settings are functional including the "Time & Date" one. Nothing is greyed or absent there as I read was the case elsewhere.

Since then I have read what appears to be duplicates on askubuntu.com as well as here. I did tried to apply proposed fixes, including fixes identifed as accepted solutions. I think I was thorough. Nothing worked.

Here is a quick replay of what I tried:

$ alias sag='sudo apt-get'

Then:

$ sag  install indicator-datetime

Reading package lists... Done
Building dependency tree       
Reading state information... Done
indicator-datetime is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
$ apt-cache policy indicator-datetime
indicator-datetime:
  Installed: 13.10.0+14.04.20140415.3-0ubuntu1
  Candidate: 13.10.0+14.04.20140415.3-0ubuntu1
  Version table:

 *** 13.10.0+14.04.20140415.3-0ubuntu1 0
        500 http://ftp.udc.es/ubuntu/ trusty/main amd64 Packages
        100 /var/lib/dpkg/status
$ sudo dpkg-reconfigure --frontend noninteractive tzdata

Current default time zone: 'Europe/Berlin'
Local time is now:      Fri Jun 26 18:35:43 CEST 2015.
Universal Time is now:  Fri Jun 26 16:35:43 UTC 2015.
$ sudo killall unity-panel-service   

exited quietly, with no visible change.

$  sudo restart lightdm

also produced no result.

$ ldd --verbose \
/usr/lib/x86_64-linux-gnu/indicator-datetime/indicator-datetime-service \

> output_ldd_indicator-datetime
$ cat output_ldd_indicator-datetime | grep -i -e "error" -e "warning" \
-e "missing"
52      libgpg-error.so.0 => /lib/x86_64-linux-gnu/libgpg-error.so.0
(0x00007f0cb6504000)
450     /lib/x86_64-linux-gnu/libgpg-error.so.0:


$ sag remove unity-control-center 1> remove-log_unity-control-center

There is nothing of note in the remove-log file as far as I could see.

Then:

$ sudo killall unity-panel-service

again exited quietly with no change at all in the unity bar.
Curiously as I tried to reinstall unity-control-center, I found it was already there, although I had just (apparently) removed it.

$  sag install unity-control-center
Reading package lists... Done
Building dependency tree       
Reading state information... Done
unity-control-center is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

Help !! In need of suggestions assistance to solve this indicator-datetime + indicator-stickynotes disappearance.

EDIT 1:

$ /usr/lib/x86_64-linux-gnu/indicator-datetime/indicator-datetime-service
Indicator-Datetime-Message: indicator-datetime exiting; failed/lost bus ownership

The message:
Indicator-Datetime-Message: indicator-datetime exiting; failed/lost bus ownershipapparently means indicator-datetime is already running.

In this AU post @Sneetsher gives another possible fix (resetting the configuration of the datetime indicator and explains where it comes from:

$ dconf reset -f /com/canonical/indicator/datetime/

That does it! No clue however as to why and how.

There remains very minor issues such as the fact that not all times in "other locations" can be correctly displayed. For instance I can simultaneaously display UTC time, Berlin and New York times but not Beijing times along with them. Before this time consuming shenanigan, I could.

EDIT 1:

It turns out that the display of additional clocks in indicator-datetime depends on the correct installatio of language packs possibly, but I really am not certain of that) related to the geographical places that corresponds to the additional clock-times. I had to reinstall packages for Chinese for Beijing's time to display correctly.

EDIT 2:

Because another indicator, indicator-stickynotes, disappeared a few minutes after indicator-datetime, and accents were not displayed correctly anymore in my skype chat-window, I suspected that it might also be related to the locale I set shortly before all my troubles began. I commented out.

# export LC_ALL=C

in my .bashrc file.

After reboot indicator-stickynotes had come back, as well as accents in my Skype chat-windows.

I am curious to know where and why the conflict arose, but I am even more pleased I could get rid of the problems.