Oh, looks like the PHP test CI is failing with WP <= 6.0.

https://github.com/woocommerce/woocommerce/actions/runs/4735579697/jobs/8406937168?pr=37795
https://github.com/woocommerce/woocommerce/actions/runs/4735579697/jobs/8406937310?pr=37795

I think the error occurred because the global variable $wp_locale_switcher has not yet been defined or initialized when we call the WC_Install::install(). Let's see if @barryhughes has any suggestions.

I think the error occurred because the global variable $wp_locale_switcher has not yet been defined or initialized when we call the WC_Install::install()

Yes, exactly—and this is really only a problem during test suite setup (because our bootstrap code runs before wp-settings.php, which is where the locale switcher is instantiated). So, I think we'd need to change two further functions.

In the case of wp_switch_to_site_locale() let's add some extra safety (note the extra check for $wp_locale_switcher):

/**
 * Switch WooCommerce to site language.
 *
 * @since 3.1.0
 */
function wc_switch_to_site_locale() {
	global $wp_locale_switcher;

	if ( function_exists( 'switch_to_locale' ) && isset( $wp_locale_switcher ) ) {
		switch_to_locale( get_locale() );

		// Filter on plugin_locale so load_plugin_textdomain loads the correct locale.
		add_filter( 'plugin_locale', 'get_locale' );

		// Init WC locale.
		WC()->load_plugin_textdomain();
	}
}

We would also need to do effectively the same thing for wc_restore_locale(). @kshojib does that all make sense and are you happy to add another commit covering those things?

Hey @chihsuan Thanks for addressing the error. @barryhughes I have added another commit with your suggestions.