Based on the discussion in
https://github.com/fish-shell/fish-shell/pull/11967
Introduce a `status language` builtin, which has subcommands for
controlling and inspecting fish's message localization status.
The motivation for this is that using only the established environment
variables `LANGUAGE`, `LC_ALL`, `LC_MESSAGES`, and `LANG` can cause
problems when fish interprets them differently from GNU gettext.
In addition, these are not well-suited for users who want to override
their normal localization settings only for fish, since fish would
propagate the values of these variables to its child processes.
Configuration via these variables still works as before, but now there
is the `status language set` command, which allows overriding the
localization configuration.
If `status language set` is used, the language precedence list will be
taken from its remaining arguments.
Warnings will be shown for invalid arguments.
Once this command was used, the localization related environment
variables are ignored.
To go back to taking the configuration from the environment variables
after `status language set` was executed, users can run `status language
unset`.
Running `status language` without arguments shows information about the
current message localization status, allowing users to better understand
how their settings are interpreted by fish.
The `status language list-available` command shows which languages are
available to choose from, which is used for completions.
This commit eliminates dependencies from the `gettext_impl` module to
code in fish's main crate, allowing for extraction of this module into
its own crate in a future commit.
Closes#12106
These tests require building with the `localize-messages` feature.
If certain translations are updated, this test might fail, either
because a message was changed in the source, or because a translation of
a message was changed, or because a translation was added in a language
which previously did not have a translation for a particular message,
and we rely on that in the test. If any of these happen, the tests need
to be updated accordingly.
Closes#11726
