[2.6.0] handle special cases for this localization cycle

[cfm]

• [x] Apply the policy on supported languages to the current set of supported_locales
  • https://docs.google.com/spreadsheets/d/1IfGqf3tgcW9PoL1h8vRJG6lTqVZuNsPYIbhG947FKMk/edit#gid=0
• [x] Review and save languages with translations contributed since v2.5.0:
  • New languages like Occitan (oc) ~has been added (any others?)~ will be pulled in by i18n_tool update-from-weblate
  • [x] Persian (fa) was updated during the Aaron Swartz Day hackathon

[cfm]

I've set up a tracking spreadsheet for applying the supported-languages policy release over release:

https://docs.google.com/spreadsheets/d/1IfGqf3tgcW9PoL1h8vRJG6lTqVZuNsPYIbhG947FKMk/edit#gid=0

The rest of these tasks must happen during the string-freeze phase of the localization cycle. I've retitled this ticket to reflect this.

Specifically, the commit l10n: sync with upstream origin/develop should be followed by downloading and committing the messages.po files for fa and oc. If these catalogs are missing from the i18n branch when it's pushed to securedrop-i18n, these translations will be clobbered in Weblate; saving them as part of the merge will preserve them.

(Neither fa or oc is likely to meet the 100% threshold for initial language support, so this action has no release implications.)

[cfm]

The above is necessary for fa, updated between translation cycles, to protect the changed .po file from i18n_tool.py translate-messages; but not for oc or any other language added between translation, since i18n_tool.py translate-messages will make no conflicting changes. Forthcoming in the pull request effecting the v2.6.0 string freeze.