Back out fix for issue #13886; it introduced a new bug in interactive readline use.
diff --git a/Modules/readline.c b/Modules/readline.c
index fd60377..4d54dad 100644
--- a/Modules/readline.c
+++ b/Modules/readline.c
@@ -1068,7 +1068,7 @@
     char *saved_locale = strdup(setlocale(LC_CTYPE, NULL));
     if (!saved_locale)
         Py_FatalError("not enough memory to save locale");
-    setlocale(LC_CTYPE, "C");
+    setlocale(LC_CTYPE, "");
 #endif
 
     if (sys_stdin != rl_instream || sys_stdout != rl_outstream) {