Previously we used to mark a key as unstranlated if its value was equal
to it in translations.json. This had an issue because it didn't allow
otherwise valid cases where key was equal to the value.
This commit solves the problem by disallowing an empty string as a valid
translation and then using the empty string as the value for all the
unstranslated keys.
Fixes#5261
compilemessages command now does all the heavy lifting by creating a
language_name_map.json file under locale directory. This file is used
by get_language_list to retrieve the require information.
Fixes: #6486
In a Zulip production environment, STATIC_ROOT points to the shared
directory that static assets are served from, and so the
compilemessages management command was trying to process every
historical version in there.