diff --git a/src/js/_enqueues/lib/ajax-response.js b/src/js/_enqueues/lib/ajax-response.js
index 659b91e023..38816f3c38 100644
--- a/src/js/_enqueues/lib/ajax-response.js
+++ b/src/js/_enqueues/lib/ajax-response.js
@@ -18,7 +18,7 @@ window.wpAjax = jQuery.extend( {
 		return r;
 	},
 	parseAjaxResponse: function( x, r, e ) { // 1 = good, 0 = strange (bad data?), -1 = you lack permission.
-		var parsed = {}, re = jQuery('#' + r).empty(), err = '', successmsg = '';
+		var parsed = {}, re = jQuery('#' + r).empty(), err = '';
 
 		if ( x && typeof x === 'object' && x.getElementsByTagName('wp_ajax') ) {
 			parsed.responses = [];
@@ -27,7 +27,6 @@ window.wpAjax = jQuery.extend( {
 				var th = jQuery(this), child = jQuery(this.firstChild), response;
 				response = { action: th.attr('action'), what: child.get(0).nodeName, id: child.attr('id'), oldId: child.attr('old_id'), position: child.attr('position') };
 				response.data = jQuery( 'response_data', child ).text();
-				successmsg += response.data;
 				response.supplemental = {};
 				if ( !jQuery( 'supplemental', child ).children().each( function() {
 					response.supplemental[this.nodeName] = jQuery(this).text();
@@ -47,14 +46,7 @@ window.wpAjax = jQuery.extend( {
 				} ).length ) { response.errors = false; }
 				parsed.responses.push( response );
 			} );
-			if ( err.length ) {
-				re.html( '<div class="error">' + err + '</div>' );
-				wp.a11y.speak( err );
-			} else {
-				re.html( '<div class="updated notice is-dismissible"><p>' + successmsg + '</p></div>');
-				jQuery(document).trigger( 'wp-updates-notice-added' );
-				wp.a11y.speak( successmsg );
-			}
+			if ( err.length ) { re.html( '<div class="error">' + err + '</div>' ); }
 			return parsed;
 		}
 		if ( isNaN(x) ) { return !re.html('<div class="error"><p>' + x + '</p></div>'); }
diff --git a/src/wp-admin/includes/ajax-actions.php b/src/wp-admin/includes/ajax-actions.php
index 191e5b54dd..1ba480f2f1 100644
--- a/src/wp-admin/includes/ajax-actions.php
+++ b/src/wp-admin/includes/ajax-actions.php
@@ -1102,19 +1102,9 @@ function wp_ajax_add_tag() {
 	$wp_list_table->single_row( $tag );
 	$parents = ob_get_clean();
 
-	require ABSPATH . 'wp-admin/includes/edit-tag-messages.php';
-
-	$message = '';
-	if ( isset( $messages[ $tax->name ][1] ) ) {
-		$message = $messages[ $tax->name ][1];
-	} elseif ( isset( $messages['_item'][1] ) ) {
-		$message = $messages['_item'][1];
-	}
-
 	$x->add(
 		array(
 			'what'         => 'taxonomy',
-			'data'         => $message,
 			'supplemental' => compact( 'parents', 'noparents' ),
 		)
 	);
diff --git a/tests/phpunit/tests/ajax/AddTag.php b/tests/phpunit/tests/ajax/AddTag.php
deleted file mode 100644
index 48b5fc5f24..0000000000
--- a/tests/phpunit/tests/ajax/AddTag.php
+++ /dev/null
@@ -1,145 +0,0 @@
-<?php
-
-/**
- * Admin ajax functions to be tested.
- */
-require_once ABSPATH . 'wp-admin/includes/ajax-actions.php';
-
-/**
- * Class for testing ajax add tag functionality.
- *
- * @group ajax
- */
-class Tests_Ajax_AddTag extends WP_Ajax_UnitTestCase {
-
-	/**
-	 * @dataProvider data_add_tag
-	 *
-	 * @ticket 42937
-	 *
-	 * @param array                 $post_data Data to populate $_POST.
-	 * @param string                $expected  Expected response.
-	 * @param array|string|callable $callback  Optional. Callback to register to 'term_updated_messages'
-	 *                                         filter. Default empty string (no callback).
-	 */
-	public function test_add_tag( array $post_data, $expected, $callback = '' ) {
-		$this->_setRole( 'administrator' );
-
-		$_POST                     = $post_data;
-		$_POST['_wpnonce_add-tag'] = wp_create_nonce( 'add-tag' );
-
-		if ( ! empty( $callback ) ) {
-			add_filter( 'term_updated_messages', $callback );
-		}
-
-		try {
-			$this->_handleAjax( 'add-tag' );
-		} catch ( WPAjaxDieContinueException $e ) {
-			unset( $e );
-		}
-
-		$this->assertSame( $expected, (string) $this->get_xml_response_taxonomy()->response_data );
-	}
-
-	/**
-	 * Data provider.
-	 *
-	 * @return array
-	 */
-	public function data_add_tag() {
-		return array(
-			'add a category'                        => array(
-				'post_data' => array(
-					'taxonomy'  => 'category',
-					'post_type' => 'post',
-					'screen'    => 'edit-category',
-					'action'    => 'add-tag',
-					'tag-name'  => 'blues',
-				),
-				'expected'  => 'Category added.',
-			),
-			'add a category with message filtering' => array(
-				'post_data' => array(
-					'taxonomy'  => 'category',
-					'post_type' => 'post',
-					'screen'    => 'edit-category',
-					'action'    => 'add-tag',
-					'tag-name'  => 'techno',
-				),
-				'expected'  => 'A new category added.',
-				'callback'  => static function( array $messages ) {
-					$messages['category'][1] = 'A new category added.';
-					return $messages;
-				},
-			),
-			'add a post_tag'                        => array(
-				'post_data' => array(
-					'taxonomy'  => 'post_tag',
-					'post_type' => 'post',
-					'screen'    => 'edit-post_tag',
-					'action'    => 'add-tag',
-					'tag-name'  => 'Louis Armstrong',
-				),
-				'expected'  => 'Tag added.',
-			),
-		);
-	}
-
-	/**
-	 * @ticket 42937
-	 */
-	public function test_adding_category_without_capability_should_error() {
-		$this->_setRole( 'subscriber' );
-
-		$_POST['taxonomy']         = 'category';
-		$_POST['post_type']        = 'post';
-		$_POST['screen']           = 'edit-category';
-		$_POST['action']           = 'add-tag';
-		$_POST['tag - name']       = 'disco';
-		$_POST['_wpnonce_add-tag'] = wp_create_nonce( 'add-tag' );
-
-		$this->expectException( 'WPAjaxDieStopException' );
-		$this->expectExceptionMessage( '-1' );
-		$this->_handleAjax( 'add-tag' );
-	}
-
-	/**
-	 * @ticket 42937
-	 */
-	public function test_adding_existing_category_should_error() {
-		$this->_setRole( 'administrator' );
-
-		wp_insert_term( 'testcat', 'category' );
-
-		$_POST = array(
-			'taxonomy'         => 'category',
-			'post_type'        => 'post',
-			'screen'           => 'edit-category',
-			'action'           => 'add-tag',
-			'tag-name'         => 'testcat',
-			'_wpnonce_add-tag' => wp_create_nonce( 'add-tag' ),
-		);
-
-		try {
-			$this->_handleAjax( 'add-tag' );
-		} catch ( WPAjaxDieContinueException $e ) {
-			unset( $e );
-		}
-
-		$expected = 'A term with the name provided already exists with this parent.';
-		$this->assertSame( $expected, (string) $this->get_xml_response_taxonomy()->wp_error );
-	}
-
-	/**
-	 * Helper method to get the taxonomy's response or error.
-	 *
-	 * @since 5.9.0
-	 *
-	 * @return SimpleXMLElement Response or error object.
-	 */
-	private function get_xml_response_taxonomy() {
-		$xml = simplexml_load_string( $this->_last_response, 'SimpleXMLElement', LIBXML_NOCDATA );
-
-		return $xml->response->taxonomy;
-	}
-}