feat(uucore): Add locale detection from LC_ALL and LC_MESSAGES

[lordeji]

TL;DR

Fix #8922.

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Implementation :

When creating the locale string, check in this order :
LC_ALL -> LC_MESSAGES -> LANG
According to the documentation on the precedence of each variable.

Important note : I did not include the LANGUAGE variable as it seems more specific to gettext and does not follow the the same pattern as the other variables (specify multiple languages).

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Testing :

I'm using the devcontainer.
For completeness, here is the result of the locale command inside the container:

LANG=
LANGUAGE=
LC_CTYPE="POSIX"
LC_NUMERIC="POSIX"
LC_TIME="POSIX"
LC_COLLATE="POSIX"
LC_MONETARY="POSIX"
LC_MESSAGES="POSIX"
LC_PAPER="POSIX"
LC_NAME="POSIX"
LC_ADDRESS="POSIX"
LC_TELEPHONE="POSIX"
LC_MEASUREMENT="POSIX"
LC_IDENTIFICATION="POSIX"
LC_ALL=

Built successfully with

cargo build

Ran tests with no error

cargo nextest run -p uucore -p coreutils --no-fail-fast

Tried all these combinations which output the correct language

[FRENCH OUTPUT]
$ LANG=fr_FR.UTF-8 ./target/debug/coreutils split --help
$ LC_MESSAGES=fr_FR.UTF-8 ./target/debug/coreutils split --help
$ LC_ALL=fr_FR.UTF-8 ./target/debug/coreutils split --help

$ LC_MESSAGES=fr_FR.UTF-8 LANG=en_US.UTF-8 ./target/debug/coreutils split --help
$ LC_ALL=fr_FR.UTF-8 LC_MESSAGES=en_US.UTF-8 ./target/debug/coreutils split --help
$ LC_ALL=fr_FR.UTF-8 LANG=en_US.UTF-8 ./target/debug/coreutils split --help


[ENGLISH OUTPUT]
$ LC_MESSAGES=en_US.UTF-8 LANG=fr_FR.UTF-8 ./target/debug/coreutils split --help
$ LC_ALL=en_US.UTF-8 LC_MESSAGES=fr_FR.UTF-8 ./target/debug/coreutils split --help
$ LC_ALL=en_US.UTF-8 LANG=fr_FR.UTF-8 ./target/debug/coreutils split --help

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Testing :

• I had to update test_env_french() test function because LANG was overidden by LC_ALL or LC_MESSAGES

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/cut/cut. tests/cut/cut is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/expr/expr. tests/expr/expr is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/join/join. tests/join/join is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/uniq/uniq. tests/uniq/uniq is passing on 'main'. Maybe you have to rebase?

[sylvestre]

It regressed a bunch of tests

[lordeji]

@sylvestre Indeed, gonna install the github actions extensions and update the PR when the test are ok (so I won't waste actions and times).

By the way, do you think a workflow should be added ?