This change switches to using `get_user_locale()` when adding the language to the Site Health debug information to ensure the user’s locale preference is reflected.
Also, `function_exists()` checks for `switch_to_locale()` and `restore_previous_locale()` were required in the plugin to support older versions of WordPress, but they are not required in core/
Props: Clorith, desrosj.
Fixes#46694.
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