Index: wp-includes/customize/class-wp-customize-theme-control.php
===================================================================
--- wp-includes/customize/class-wp-customize-theme-control.php	(revision 45112)
+++ wp-includes/customize/class-wp-customize-theme-control.php	(working copy)
@@ -103,10 +103,7 @@
 			<# if ( data.theme.active ) { #>
 				<div class="theme-id-container">
 					<h3 class="theme-name" id="{{ data.section }}-{{ data.theme.id }}-name">
-						<?php
-						/* translators: %s: theme name */
-						printf( __( '<span>Previewing:</span> %s' ), '{{ data.theme.name }}' );
-						?>
+						<span><?php _e( 'Previewing:' ); ?></span> {{ data.theme.name }}
 					</h3>
 					<div class="theme-actions">
 						<button type="button" class="button button-primary customize-theme" aria-label="<?php echo esc_attr( $customize_label ); ?>"><?php _e( 'Customize' ); ?></button>