Renew Translation Platform

There is no active developement in Zanata project since September 2018 anymore. We should think about replace the OpenStack Translation Platform in Train Cycle if there are no changes on the maintenance level. Which requirements should have the new platform:
* web-based
* authentification with OpenStackID
* user management in language groups with permissions in language owner, translator, and reviewer
* metrics for stats (user activities, translation progress)
* projects, documents in different version (branches)
* upload/download po files
* REST API for all of them
* support for gettext, txt, xml, file
* copy & merge versions
* set versions read-only
* translation Memory and TM distribution (connect to other TM services)
* backend connection to Machine Translation Service (Deepl, Google Translate, Microsoft Translate)

Thanks to AI has Machine Translation made a great progress and it's time to step in. The OpenStack Community can help to determine the language vocabulary in the cloud.

Solution overview:
Pootle: http://docs.translatehouse.org/projects/pootle/en/latest/index.html
Poedit: https://poedit.net/ (client)
Poeditor: https://poeditor.com/ (commercial)
Transiflex: https://www.transifex.com/ (commercial)
Weblate: https://weblate.org/
Pontoon: https://pontoon.mozilla.org/

Gala 2018 Boston Talks: https://www.gala-global.org/conference/gala-2018-boston/gala-annual-conference-videos

Previous activities:
https://etherpad.openstack.org/p/translation-tools-comparation
http://lists.openstack.org/pipermail/openstack-i18n/2014-October/000828.html)