diff --git src/wp-admin/customize.php src/wp-admin/customize.php
index 0a1f9b3..c90f114 100644
--- src/wp-admin/customize.php
+++ src/wp-admin/customize.php
@@ -191,9 +191,9 @@ do_action( 'customize_controls_print_scripts' );
 				<?php endforeach; ?>
 			</div>
 			<?php endif; ?>
-			<button type="button" class="collapse-sidebar button" aria-expanded="true" aria-label="<?php esc_attr_e( 'Hide Controls' ); ?>">
+			<button type="button" class="collapse-sidebar button" aria-expanded="true" aria-label="<?php echo esc_attr( _x( 'Hide Controls', 'label for hide controls button without length constraints' ) ); ?>">
 				<span class="collapse-sidebar-arrow"></span>
-				<span class="collapse-sidebar-label"><?php _e( 'Hide Controls' ); ?></span>
+				<span class="collapse-sidebar-label"><?php _ex( 'Hide Controls', 'short (~12 characters) label for hide controls button' ); ?></span>
 			</button>
 		</div>
 	</form>
diff --git src/wp-includes/script-loader.php src/wp-includes/script-loader.php
index c64920a..fadfb28 100644
--- src/wp-includes/script-loader.php
+++ src/wp-includes/script-loader.php
@@ -467,8 +467,8 @@ function wp_default_scripts( &$scripts ) {
 		'notAllowed'         => __( 'Sorry, you are not allowed to customize this site.' ),
 		'previewIframeTitle' => __( 'Site Preview' ),
 		'loginIframeTitle'   => __( 'Session expired' ),
-		'collapseSidebar'    => __( 'Hide Controls' ),
-		'expandSidebar'      => __( 'Show Controls' ),
+		'collapseSidebar'    => _x( 'Hide Controls', 'label for hide controls button without length constraints' ),
+		'expandSidebar'      => _x( 'Show Controls', 'label for hide controls button without length constraints' ),
 		'untitledBlogName'   => __( '(Untitled)' ),
 		// Used for overriding the file types allowed in plupload.
 		'allowedFiles'       => __( 'Allowed Files' ),