Translation Server: Clearify languages in weblate-settings

In order be able to enable/disable languages easily, we should have one place to define the supported languages.
As master reference I want to use manifests/weblate/languages.pp (in puppet-tails).

But the languages are not used for the templates/weblate/settings.py.erb (puppet-tails). Even worse the LANGUAGES list differs a lot from the languages in languages.pp. Or is the LANGUAGES list in weblate settings the list of supported translations for the Weblate interface?

https://translate.tails.boum.org/languages/ in contrast output the list that we have in manifests/weblate/languages.pp.

Parent Task: #16521 (closed)

Original created by @Hefee on 16523 (Redmine)

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