diff -r 68d653f9a2c9 Lib/locale.py
--- a/Lib/locale.py	Wed May 13 11:25:40 2015 -0400
+++ b/Lib/locale.py	Fri May 15 11:34:37 2015 +0200
@@ -472,6 +472,8 @@
         return tuple(code.split('.')[:2])
     elif code == 'C':
         return None, None
+    elif sys.platform == 'darwin' and code == 'UTF-8':
+        return None, 'UTF-8'
     raise ValueError, 'unknown locale: %s' % localename
 
 def _build_localename(localetuple):