Index: src/wp-admin/includes/class-custom-background.php
===================================================================
--- src/wp-admin/includes/class-custom-background.php	(revision 55860)
+++ src/wp-admin/includes/class-custom-background.php	(working copy)
@@ -63,7 +63,14 @@
 	 * @since 3.0.0
 	 */
 	public function init() {
-		$page = add_theme_page( __( 'Background' ), __( 'Background' ), 'edit_theme_options', 'custom-background', array( $this, 'admin_page' ) );
+		$page = add_theme_page(
+			_x( 'Background', 'custom background' ),
+			_x( 'Background', 'custom background' ),
+			'edit_theme_options',
+			'custom-background',
+			array( $this, 'admin_page' )
+		);
+
 		if ( ! $page ) {
 			return;
 		}
Index: src/wp-admin/includes/class-custom-image-header.php
===================================================================
--- src/wp-admin/includes/class-custom-image-header.php	(revision 55860)
+++ src/wp-admin/includes/class-custom-image-header.php	(working copy)
@@ -71,7 +71,13 @@
 	 * @since 2.1.0
 	 */
 	public function init() {
-		$page = add_theme_page( __( 'Header' ), __( 'Header' ), 'edit_theme_options', 'custom-header', array( $this, 'admin_page' ) );
+		$page = add_theme_page(
+			_x( 'Header', 'custom image header' ),
+			_x( 'Header', 'custom image header' ),
+			'edit_theme_options',
+			'custom-header',
+			array( $this, 'admin_page' )
+		);
 
 		if ( ! $page ) {
 			return;
Index: src/wp-admin/menu.php
===================================================================
--- src/wp-admin/menu.php	(revision 55860)
+++ src/wp-admin/menu.php	(working copy)
@@ -230,12 +230,12 @@
 
 if ( current_theme_supports( 'custom-header' ) && current_user_can( 'customize' ) ) {
 	$customize_header_url      = add_query_arg( array( 'autofocus' => array( 'control' => 'header_image' ) ), $customize_url );
-	$submenu['themes.php'][15] = array( __( 'Header' ), $appearance_cap, esc_url( $customize_header_url ), '', 'hide-if-no-customize' );
+	$submenu['themes.php'][15] = array( _x( 'Header', 'custom image header' ), $appearance_cap, esc_url( $customize_header_url ), '', 'hide-if-no-customize' );
 }
 
 if ( current_theme_supports( 'custom-background' ) && current_user_can( 'customize' ) ) {
 	$customize_background_url  = add_query_arg( array( 'autofocus' => array( 'control' => 'background_image' ) ), $customize_url );
-	$submenu['themes.php'][20] = array( __( 'Background' ), $appearance_cap, esc_url( $customize_background_url ), '', 'hide-if-no-customize' );
+	$submenu['themes.php'][20] = array( _x( 'Background', 'custom background' ), $appearance_cap, esc_url( $customize_background_url ), '', 'hide-if-no-customize' );
 }
 
 unset( $customize_url );
Index: src/wp-includes/admin-bar.php
===================================================================
--- src/wp-includes/admin-bar.php	(revision 55860)
+++ src/wp-includes/admin-bar.php	(working copy)
@@ -1052,7 +1052,7 @@
 			array(
 				'parent' => 'appearance',
 				'id'     => 'background',
-				'title'  => __( 'Background' ),
+				'title'  => _x( 'Background', 'custom background' ),
 				'href'   => admin_url( 'themes.php?page=custom-background' ),
 				'meta'   => array(
 					'class' => 'hide-if-customize',
@@ -1066,7 +1066,7 @@
 			array(
 				'parent' => 'appearance',
 				'id'     => 'header',
-				'title'  => __( 'Header' ),
+				'title'  => _x( 'Header', 'custom image header' ),
 				'href'   => admin_url( 'themes.php?page=custom-header' ),
 				'meta'   => array(
 					'class' => 'hide-if-customize',
Index: src/wp-includes/block-template-utils.php
===================================================================
--- src/wp-includes/block-template-utils.php	(revision 55860)
+++ src/wp-includes/block-template-utils.php	(working copy)
@@ -65,7 +65,7 @@
 	$default_area_definitions = array(
 		array(
 			'area'        => WP_TEMPLATE_PART_AREA_UNCATEGORIZED,
-			'label'       => __( 'General' ),
+			'label'       => _x( 'General', 'template part area' ),
 			'description' => __(
 				'General templates often perform a specific role like displaying post content, and are not tied to any particular area.'
 			),
@@ -74,7 +74,7 @@
 		),
 		array(
 			'area'        => WP_TEMPLATE_PART_AREA_HEADER,
-			'label'       => __( 'Header' ),
+			'label'       => _x( 'Header', 'template part area' ),
 			'description' => __(
 				'The Header template defines a page area that typically contains a title, logo, and main navigation.'
 			),
@@ -83,7 +83,7 @@
 		),
 		array(
 			'area'        => WP_TEMPLATE_PART_AREA_FOOTER,
-			'label'       => __( 'Footer' ),
+			'label'       => _x( 'Footer', 'template part area' ),
 			'description' => __(
 				'The Footer template defines a page area that typically contains site credits, social links, or any other combination of blocks.'
 			),