We had Prettier pinned because of https://github.com/prettier/prettier/issues/5529. Since that bug is fixed, unpinning.
Prettier now supports YAML, so this applies Prettier to all .yml except for translations, which should not be edited directly anyway.
The FallbackLocaleList object tells I18n::Backend::Fallbacks what order the
languages should be attempted in. Because of the translate_accelerator patch,
the SiteSetting.default_locale is *not* guaranteed to be fully loaded after the
server starts, so a call to ensure_loaded! is added after the locale is set for
the current user.
The declarations of config.i18n.fallbacks = true in the environment files were
actually garbage, because the I18n.default_locale was
SiteSetting.default_locale, so there was nothing to fall back to. *derp*
