I'm not sure that locale.bindtextdomain() uses the right encoding neither. I propose the following fix:

diff --git a/Modules/_localemodule.c b/Modules/_localemodule.c
index 324b694b83..1de17d3620 100644
--- a/Modules/_localemodule.c
+++ b/Modules/_localemodule.c
@@ -555,7 +555,7 @@ PyIntl_bindtextdomain(PyObject* self,PyObject*args)
         PyErr_SetFromErrno(PyExc_OSError);
         return NULL;
     }
-    result = PyUnicode_DecodeLocale(current_dirname, NULL);
+    result = PyUnicode_DecodeFSDefault(current_dirname);
     Py_XDECREF(dirname_bytes);
     return result;
 }