The hook is applied in file wp-content\plugins\woocommerce-currency-switcher\views\shortcodes\woocs.php for the text manipulation in the switchers drop-down.
//return "Hello " . $currency_name . '!!';
Use it by your own logic.
How can i make sure that there is only a currency symbol in the dropdown without editing the plugin files, so updates are possible. DDSlick dropdown preferred