Formats from Greeter not respected

Both 3.14 and bc022ef71e and affected:

• When I start Tails in French/France, I get A4 by default in LibreOffice
• When I start Tails in English/United States, I get Letter by default in LibreOffice

So far so good, but:

• When I start Tails in French/United States, I get A4 by default in LibreOffice
• When I start Tails in English/France, I get Letter by default in LibreOffice

Once this is fixed, tech writers will have to update /doc/first_steps/startup_options/US_calendar_in_Russian.png.

Feature Branch: https://salsa.debian.org/tails-team/tails/merge_requests/39/commits

Related issues

• Related to #14544
• Blocks #16209
• Blocked by #16095 (closed)

Original created by @sajolida on 16806 (Redmine)