Manually change text or translate text string for PMPro Approvals Add On using the gettext filter.

change-text-for-pmpro-approvals.php

<?php
/**
 * This recipe changes localized text strings for
 * Paid Memberships Pro Approvals Add On using the gettext filter.
 *
 * @link http://codex.wordpress.org/Plugin_API/Filter_Reference/gettext
 *
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */

function change_text_for_pmpro_approvals( $translated_text, $text, $domain ) {
	// only do this in admin
	if ( ! defined( 'PMPRO_APP_DIR' ) ) {
		return $translated_text;
	}
	if ( 'pmpro-approvals' !== $domain ) {
		return $translated_text;
	}

	switch ( $translated_text ) {
		case 'Thank you for your membership to %1$s. Your %2$s membership status is: <b>%3$s</b>.':
			//     var_dump( $translated_text );
			//     return null;
			// break;
			$translated_text = __( 'Merci de votre adhésion à %1$s. Votre statut de membre %2$s est: <b> %3$s </b>.', 'pmpro-approvals' );
			break;
	}
	return $translated_text;
}
add_filter( 'gettext', 'change_text_for_pmpro_approvals', 10, 3 );