diff --git a/mercurial/pycompat.py b/mercurial/pycompat.py
--- a/mercurial/pycompat.py
+++ b/mercurial/pycompat.py
@@ -13,6 +13,7 @@ from __future__ import absolute_import
 import getopt
 import inspect
 import json
+import locale
 import os
 import shlex
 import sys
@@ -93,6 +94,26 @@ def rapply(f, xs):
     return _rapply(f, xs)
 
 
+# Passing the '' locale means that the locale should be set according to the
+# user settings (environment variables).
+# Python sometimes avoids setting the global locale settings. When interfacing
+# with C code (e.g. the curses module or the Subversion bindings), the global
+# locale settings must be initialized correctly. Python 2 does not initialize
+# the global locale settings on interpreter startup. Python 3 sometimes
+# initializes LC_CTYPE, but not consistently at least on Windows. Therefore we
+# explicitly initialize it to get consistent behavior if it's not already
+# initialized. Since CPython commit 177d921c8c03d30daa32994362023f777624b10d,
+# LC_CTYPE is always initialized. If we require Python 3.8+, we should re-check
+# if we can remove this code.
+if locale.setlocale(locale.LC_CTYPE, None) == 'C':
+    try:
+        locale.setlocale(locale.LC_CTYPE, '')
+    except locale.Error:
+        # The likely case is that the locale from the environment variables is
+        # unknown.
+        pass
+
+
 if ispy3:
     import builtins
     import codecs