This avoids the importing the heavy Gettext backend in some places
and makes it clearer what’s actually used in the project and what’s
used by the Gettext library.
With the to-be-pulled-in Gettext API change this split
will be even more helpful for code clarity.
As a bonus documentation is improved and
the unused locale_or_default function removed.
elixir gettext current does not fully support fallback to another language [0].
But it might in the future. We adapt it so that all languages in Accept-Language
headers are received by Pleroma.Web.Gettext. User.languages is now a comma-separated
list.
[0]: https://github.com/elixir-gettext/gettext/issues/303
For an example, here, zh is not supported, but zh_Hans and zh_Hant
are. If the user asks for zh, we should choose a variant for them
instead of fallbacking to default.
Some browsers (e.g. Firefox) does not allow users to customize
their language codes. For example, there is no zh-Hans, but only
zh, zh-CN, zh-TW, zh-HK, etc. This provides a workaround for
those users suffering from bad design decisions.
