diff -r 064b29dde096 Lib/idlelib/NEWS.txt
--- a/Lib/idlelib/NEWS.txt	Tue Jun 21 18:41:38 2016 -0400
+++ b/Lib/idlelib/NEWS.txt	Tue Jun 21 23:04:49 2016 -0400
@@ -58,7 +58,7 @@
   Original patch by Saimadhav Heblikar.
 
 - Issue #18410: Add test for IDLE's search dialog.
-  Original patch by Westley Martínez.
+  Original patch by Westley Martínez.
 
 - Issue #21703: Add test for undo delegator.  Patch mostly by
   Saimadhav Heblikar .
@@ -76,7 +76,7 @@
 - Issue #25507: fix incorrect change in IOBinding that prevented printing.
   Augment IOBinding htest to include all major IOBinding functions.
 
-- Issue #25905: Revert unwanted conversion of ' to ’ RIGHT SINGLE QUOTATION
+- Issue #25905: Revert unwanted conversion of ' to ’ RIGHT SINGLE QUOTATION
   MARK in README.txt and open this and NEWS.txt with 'ascii'.
   Re-encode CREDITS.txt to utf-8 and open it with 'utf-8'.
 
diff -r 064b29dde096 Lib/idlelib/help_about.py
--- a/Lib/idlelib/help_about.py	Tue Jun 21 18:41:38 2016 -0400
+++ b/Lib/idlelib/help_about.py	Tue Jun 21 23:04:49 2016 -0400
@@ -130,7 +130,7 @@
         self.display_file_text('About - Readme', 'README.txt', 'ascii')
 
     def ShowIDLENEWS(self):
-        self.display_file_text('About - NEWS', 'NEWS.txt', 'ascii')
+        self.display_file_text('About - NEWS', 'NEWS.txt', 'utf-8')
 
     def display_printer_text(self, title, printer):
         printer._Printer__setup()
diff -r 064b29dde096 Lib/idlelib/idle_test/test_help_about.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Lib/idlelib/idle_test/test_help_about.py	Tue Jun 21 23:04:49 2016 -0400
@@ -0,0 +1,52 @@
+'''Test idlelib.help_about.
+
+Coverage:
+'''
+from idlelib import help_about
+from idlelib import textview
+from idlelib.idle_test.mock_idle import Func
+from idlelib.idle_test.mock_tk import Mbox_func
+import unittest
+
+About = help_about.AboutDialog
+class Dummy_about_dialog():
+    # Dummy class for testing file display functions.
+    idle_credits = About.ShowIDLECredits
+    idle_readme = About.ShowIDLEAbout
+    idle_news = About.ShowIDLENEWS
+    # Called by the above
+    display_file_text = About.display_file_text
+
+
+class DisplayFileTest(unittest.TestCase):
+    dialog = Dummy_about_dialog()
+
+    @classmethod
+    def setUpClass(cls):
+        cls.orig_error = textview.showerror
+        cls.orig_view = textview.view_text
+        cls.error = Mbox_func()
+        cls.view = Func()
+        textview.showerror = cls.error
+        textview.view_text = cls.view
+        cls.About = Dummy_about_dialog()
+
+    @classmethod
+    def tearDownClass(cls):
+        textview.showerror = cls.orig_error
+        textview.view_text = cls.orig_view
+
+    def test_file_isplay(self):
+        for handler in (self.dialog.idle_credits,
+                        self.dialog.idle_readme,
+                        self.dialog.idle_news):
+            self.error.message = ''
+            self.view.called = False
+            with self.subTest(handler=handler):
+                handler()
+                self.assertEqual(self.error.message, '')
+                self.assertEqual(self.view.called, True)
+
+
+if __name__ == '__main__':
+    unittest.main(verbosity=2)
diff -r 064b29dde096 Lib/idlelib/textview.py
--- a/Lib/idlelib/textview.py	Tue Jun 21 18:41:38 2016 -0400
+++ b/Lib/idlelib/textview.py	Tue Jun 21 23:04:49 2016 -0400
@@ -4,7 +4,7 @@
 
 from tkinter import *
 from tkinter.ttk import Scrollbar
-import tkinter.messagebox as tkMessageBox
+from tkinter.messagebox import showerror
 
 class TextViewer(Toplevel):
     """A simple text viewer dialog for IDLE
@@ -74,9 +74,13 @@
         with open(filename, 'r', encoding=encoding) as file:
             contents = file.read()
     except IOError:
-        tkMessageBox.showerror(title='File Load Error',
-                               message='Unable to load file %r .' % filename,
-                               parent=parent)
+        showerror(title='File Load Error',
+                  message='Unable to load file %r .' % filename,
+                  parent=parent)
+    except UnicodeDecodeError as err:
+        showerror(title='Unicode Decode Error',
+                  message=str(err),
+                  parent=parent)
     else:
         return view_text(parent, title, contents, modal)