diff -r eee959fee5f5 Lib/_bootlocale.py
--- a/Lib/_bootlocale.py	Sat May 07 21:13:50 2016 +0300
+++ b/Lib/_bootlocale.py	Sat May 21 10:48:27 2016 +0200
@@ -15,6 +15,13 @@
         _locale.CODESET
     except AttributeError:
         def getpreferredencoding(do_setlocale=True):
+            # Avoid importing locale and its dependencies when none of the
+            # locale environment variables is set.
+            import os
+            if (set(os.environ).isdisjoint(('LC_ALL', 'LC_CTYPE', 'LANG',
+                                            'LANGUAGE'))):
+                return 'ascii'
+
             # This path for legacy systems needs the more complex
             # getdefaultlocale() function, import the full locale module.
             import locale