bpo-41152: IDLE: always use UTF-8 for standard IO streams (GH-21214)

(cherry picked from commit 2515a28230b1a011205f30263da6b01c6bd167a3)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
diff --git a/Lib/idlelib/NEWS.txt b/Lib/idlelib/NEWS.txt
index c270fcb..7ae29af 100644
--- a/Lib/idlelib/NEWS.txt
+++ b/Lib/idlelib/NEWS.txt
@@ -3,6 +3,9 @@
 ======================================
 
 
+bpo-41152: The encoding of ``stdin``, ``stdout`` and ``stderr`` in IDLE
+is now always UTF-8.
+
 bpo-41144: Make Open Module open a special module such as os.path.
 
 bpo-40723: Make test_idle pass when run after import.