The icudtl.dat is also needed by helper app.

atom.gyp

@@ -386,6 +386,15 @@
                 '<@(locale_dirs)',
               ],
             },
+              # Link the icudtl.dat file to the Helper app, which is needed
+              # by the V8 of Helper too.
+            {
+              'postbuild_name' : 'Link icudtl.dat to Helper App',
+              'action': [
+                'tools/mac/link_file_to_helper.sh',
+                'Resources/icudtl.dat',
+              ],
+            },
           ]
         }, {  # OS=="mac"
           'dependencies': [

tools/mac/link_file_to_helper.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+
+# Copyright (c) 2014 GitHub, Inc. All rights reserved.
+# Use of this source code is governed by the MIT license that can be
+# found in the LICENSE file.
+
+# usage: link_file_to_helper.sh relative-path-to-Contents
+# This script links a file from the helper app to the main app.
+
+FILE_PATH=$1
+HELPER_CONTENTS_FOLDER_PATH="$BUILT_PRODUCTS_DIR/$CONTENTS_FOLDER_PATH/Frameworks/$PRODUCT_NAME Helper.app/Contents"
+
+PARENT="`dirname "$HELPER_CONTENTS_FOLDER_PATH/$FILE_PATH"`"
+if [[ ! -d "$PARENT" ]]; then
+  mkdir -p "$PARENT"
+fi
+
+cd "$HELPER_CONTENTS_FOLDER_PATH"
+ln -s "../../../../$FILE_PATH" "$FILE_PATH"