Translate credit card fields placeholders for WooCommerce Stripe

Paste the following in functions.php:

add_filter( 'wc_stripe_elements_options', 'wc_update_locale_in_stripe_element_options' );
function wc_update_locale_in_stripe_element_options( $options ) {
    return array_merge(
        $options,
        array(
            'locale' => get_locale(),
        )
    );
};

get_locale() will automatically translate the fields to the browser’s language. For a specific language, use language code between quotation marks, for example ‘fr’ for French.

Source: https://docs.woocommerce.com/document/stripe/#section-33