s/directory/folder/ to match it with the plural case.

chrome/app/chromeos_strings.grdp

 <?xml version="1.0" encoding="utf-8"?>
 <!-- ChromeOS-specific strings (included from generated_resources.grd).
      Everything in this file is wrapped in <if expr="chromeos">. -->
 <grit-part>
   <message name="IDS_EMPTY_STRING" desc="Empty string, exist only to make code generic. No translation required.">
   </message>
   <!-- Idle logout dialog for retail mode -->
   <message name="IDS_IDLE_LOGOUT_TITLE" desc="Dialog title for the idle logout dialog. Used in retail mode only.">
     Are you still there?
   </message>
@@ skipping 705 matching lines @@
     Select one or more files
   </message>
   <message name="IDS_FILE_BROWSER_SELECT_SAVEAS_FILE_TITLE" desc="Select saveas file title.">
     Save file as
   </message>
 
   <message name="IDS_FILE_BROWSER_ONE_FILE_SELECTED" desc="One file selected.">
     1 file selected
   </message>
   <message name="IDS_FILE_BROWSER_ONE_DIRECTORY_SELECTED" desc="One directory selected.">
-    1 directory selected
+    1 folder selected
   </message>
   <message name="IDS_FILE_BROWSER_MANY_FILES_SELECTED" desc="Many files selected.">
     <ph name="SELCTED_FILE_COUNT">$1<ex>13</ex></ph> files selected
   </message>
   <message name="IDS_FILE_BROWSER_MANY_DIRECTORIES_SELECTED" desc="Many directories selected.">
     <ph name="SELCTED_FOLDERS_COUNT">$1<ex>2</ex></ph> folders selected
   </message>
   <message name="IDS_FILE_BROWSER_MANY_ENTRIES_SELECTED" desc="Many items (both files and directories) selected.">
     <ph name="SELCTED_FILES_COUNT">$1<ex>21</ex></ph> items selected
   </message>
@@ skipping 5846 matching lines @@
   <message name="IDS_ARC_SERVER_COMMUNICATION_ERROR" desc="Android sign-in error because of server communication error">
     Server communication error
   </message>
   <message name="IDS_FLAGS_ENABLE_IME_MENU_NAME" desc="Name of the about: flag for enabling opt-in IME menu.">
     Enable opt-in IME menu
     </message>
   <message name="IDS_FLAGS_ENABLE_IME_MENU_DESCRIPTION" desc="Description of the about: flag for enabling opt-in IME menu.">
     Enable access to the new IME menu in the Language Settings page.
   </message>
 </grit-part>