Do stats on the languages in which people start Tails

When Tails checks for security upgrades, it tries to fetch /security/index.$LANG.atom where $LANG is the language of the session.

Studying which languages people use Tails in will be useful to work on #16095 (closed) and, in general, to know our user base a bit more.

Original created by @sajolida on 17002 (Redmine)

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