Retrieves the localized stylesheet URI.

The stylesheet directory for the localized stylesheet files are located, by
default, in the base theme directory. The name of the locale file will be the
locale followed by ‘.css’. If that does not exist, then the text direction
stylesheet will be checked for existence, for example ‘ltr.css’.

The theme may change the location of the stylesheet directory by either using
the {@see ‘stylesheet_directory_uri’} or {@see ‘locale_stylesheet_uri’} filters.

If you want to change the location of the stylesheet files for the entire
WordPress workflow, then change the former. If you just have the locale in a
separate folder, then change the latter.

function get_locale_stylesheet_uri() {
	global $wp_locale;
	$stylesheet_dir_uri = get_stylesheet_directory_uri();
	$dir                = get_stylesheet_directory();
	$locale             = get_locale();
	if ( file_exists( "$dir/$locale.css" ) ) {
		$stylesheet_uri = "$stylesheet_dir_uri/$locale.css";
	} elseif ( ! empty( $wp_locale->text_direction ) && file_exists( "$dir/{$wp_locale->text_direction}.css" ) ) {
		$stylesheet_uri = "$stylesheet_dir_uri/{$wp_locale->text_direction}.css";
	} else {
		$stylesheet_uri = '';
	}
	/**
	 * Filters the localized stylesheet URI.
	 *
	 * @since 2.1.0
	 *
	 * @param string $stylesheet_uri     Localized stylesheet URI.
	 * @param string $stylesheet_dir_uri Stylesheet directory URI.
	 */
	return apply_filters( 'locale_stylesheet_uri', $stylesheet_uri, $stylesheet_dir_uri );
}