Index: wp-admin/includes/theme-install.php
===================================================================
--- wp-admin/includes/theme-install.php	(revision 21318)
+++ wp-admin/includes/theme-install.php	(working copy)
@@ -64,7 +64,19 @@
 	<option value="author" <?php selected('author', $type) ?>><?php _e('Author'); ?></option>
 	<option value="tag" <?php selected('tag', $type) ?>><?php _ex('Tag', 'Theme Installer'); ?></option>
 	</select>
-	<label class="screen-reader-text" for="s"><?php printf( __("Search by %s"), ( $type == 'term' ? __( 'keyword' ) : $type ) ); ?></label>
+	<label class="screen-reader-text" for="s"><?php
+	  switch ( $type ) {
+		  case 'term':
+			  _e( 'Search by keyword' );
+			  break;
+		  case 'author':
+			  _e( 'Search by author' );
+			  break;
+		  case 'tag':
+			  _e( 'Search by tag' );
+			  break;
+	  }
+	?></label>
 	<?php else : ?>
 	<label class="screen-reader-text" for="s"><?php _e("Search by keyword"); ?></label>
 	<?php endif; ?>