diff --git a/Doc/library/locale.rst b/Doc/library/locale.rst

index b04442bc162..9a0c570533a 100644

--- a/Doc/library/locale.rst

+++ b/Doc/library/locale.rst

@@ -147,6 +147,16 @@ The :mod:`locale` module defines the following exception and functions:

    | ``CHAR_MAX`` | Nothing is specified in this locale.    |

    +--------------+-----------------------------------------+

+   The function sets temporarily the ``LC_CTYPE`` locale to the ``LC_NUMERIC``

+   locale to decode ``decimal_point`` and ``thousands_sep`` byte strings if

+   they are non-ASCII or longer than 1 byte, and the ``LC_NUMERIC`` locale is

+   different than the ``LC_CTYPE`` locale. This temporary change affects other

+   threads.

+

+   .. versionchanged:: 3.6.5

+      The function now sets temporarily the ``LC_CTYPE`` locale to the

+      ``LC_NUMERIC`` locale in some cases.

+

 .. function:: nl_langinfo(option)

diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst

index 196a4c00056..d8a1647e8b5 100644

--- a/Doc/library/stdtypes.rst

+++ b/Doc/library/stdtypes.rst

@@ -1599,6 +1599,20 @@ expression support in the :mod:`re` module).

    See :ref:`formatstrings` for a description of the various formatting options

    that can be specified in format strings.

+   .. note::

+      When formatting a number (:class:`int`, :class:`float`, :class:`float`

+      and subclasses) with the ``n`` type (ex: ``'{:n}'.format(1234)``), the

+      function sets temporarily the ``LC_CTYPE`` locale to the ``LC_NUMERIC``

+      locale to decode ``decimal_point`` and ``thousands_sep`` fields of

+      :c:func:`localeconv` if they are non-ASCII or longer than 1 byte, and the

+      ``LC_NUMERIC`` locale is different than the ``LC_CTYPE`` locale. This

+      temporary change affects other threads.

+

+   .. versionchanged:: 3.6.5

+      When formatting a number with the ``n`` type, the function sets

+      temporarily the ``LC_CTYPE`` locale to the ``LC_NUMERIC`` locale in some

+      cases.

+

 .. method:: str.format_map(mapping)

diff --git a/Doc/whatsnew/3.6.rst b/Doc/whatsnew/3.6.rst

index 847b50140a6..f83508c9250 100644

--- a/Doc/whatsnew/3.6.rst

+++ b/Doc/whatsnew/3.6.rst

@@ -2346,3 +2346,11 @@ It has been replaced by the new ``make regen-all`` target.

 (Contributed by Victor Stinner in :issue:`23404`.)

 .. versionchanged:: 3.6.2

+

+

+Notable changes in Python 3.6.5

+===============================

+

+The :func:`locale.localeconv` function now sets temporarily the ``LC_CTYPE``

+locale to the ``LC_NUMERIC`` locale in some cases.

+(Contributed by Victor Stinner in :issue:`31900`.)

diff --git a/Include/fileutils.h b/Include/fileutils.h

index 900c70faad7..875715df97a 100644

--- a/Include/fileutils.h

+++ b/Include/fileutils.h

@@ -119,6 +119,11 @@ PyAPI_FUNC(int) _Py_get_blocking(int fd);

 PyAPI_FUNC(int) _Py_set_blocking(int fd, int blocking);

 #endif   /* !MS_WINDOWS */

+PyAPI_FUNC(int) _Py_GetLocaleconvNumeric(

+    PyObject **decimal_point,

+    PyObject **thousands_sep,

+    const char **grouping);

+

 #endif   /* Py_LIMITED_API */

 #ifdef __cplusplus

diff --git a/Modules/_localemodule.c b/Modules/_localemodule.c

index 71c9146ccb8..95b370b1ad0 100644

--- a/Modules/_localemodule.c

+++ b/Modules/_localemodule.c

@@ -171,12 +171,6 @@ PyLocale_localeconv(PyObject* self)

         RESULT(#i, x); \

     } while (0)

-    /* Numeric information */

-    RESULT_STRING(decimal_point);

-    RESULT_STRING(thousands_sep);

-    x = copy_grouping(l->grouping);

-    RESULT("grouping", x);

-

     /* Monetary information */

     RESULT_STRING(int_curr_symbol);

     RESULT_STRING(currency_symbol);

@@ -195,6 +189,32 @@ PyLocale_localeconv(PyObject* self)

     RESULT_INT(n_sep_by_space);

     RESULT_INT(p_sign_posn);

     RESULT_INT(n_sign_posn);

+

+    /* Numeric information */

+    PyObject *decimal_point, *thousands_sep;

+    const char *grouping;

+    if (_Py_GetLocaleconvNumeric(&decimal_point,

+                                 &thousands_sep,

+                                 &grouping) < 0) {

+        goto failed;

+    }

+

+    if (PyDict_SetItemString(result, "decimal_point", decimal_point) < 0) {

+        Py_DECREF(decimal_point);

+        Py_DECREF(thousands_sep);

+        goto failed;

+    }

+    Py_DECREF(decimal_point);

+

+    if (PyDict_SetItemString(result, "thousands_sep", thousands_sep) < 0) {

+        Py_DECREF(thousands_sep);

+        goto failed;

+    }

+    Py_DECREF(thousands_sep);

+

+    x = copy_grouping(grouping);

+    RESULT("grouping", x);

+

     return result;

   failed:

diff --git a/Python/fileutils.c b/Python/fileutils.c

index 97505e5bc6d..14dd81b03f0 100644

--- a/Python/fileutils.c

+++ b/Python/fileutils.c

@@ -1597,3 +1597,80 @@ _Py_set_blocking(int fd, int blocking)

     return -1;

 }

 #endif

+

+

+int

+_Py_GetLocaleconvNumeric(PyObject **decimal_point, PyObject **thousands_sep,

+                         const char **grouping)

+{

+    int res = -1;

+

+    struct lconv *lc = localeconv();

+

+    int change_locale = 0;

+    if (decimal_point != NULL &&

+        (strlen(lc->decimal_point) > 1 || ((unsigned char)lc->decimal_point[0]) > 127))

+    {

+        change_locale = 1;

+    }

+    if (thousands_sep != NULL &&

+        (strlen(lc->thousands_sep) > 1 || ((unsigned char)lc->thousands_sep[0]) > 127))

+    {

+        change_locale = 1;

+    }

+

+    /* Keep a copy of the LC_CTYPE locale */

+    char *oldloc = NULL, *loc = NULL;

+    if (change_locale) {

+        oldloc = setlocale(LC_CTYPE, NULL);

+        if (!oldloc) {

+            PyErr_SetString(PyExc_RuntimeWarning, "faild to get LC_CTYPE locale");

+            return -1;

+        }

+

+        oldloc = _PyMem_Strdup(oldloc);

+        if (!oldloc) {

+            PyErr_NoMemory();

+            return -1;

+        }

+

+        loc = setlocale(LC_NUMERIC, NULL);

+        if (loc != NULL && strcmp(loc, oldloc) == 0) {

+            loc = NULL;

+        }

+

+        if (loc != NULL) {

+            /* Only set the locale temporarilty the LC_CTYPE locale

+               if LC_NUMERIC locale is different than LC_CTYPE locale and

+               decimal_point and/or thousands_sep are non-ASCII or longer than

+               1 byte */

+            setlocale(LC_CTYPE, loc);

+        }

+    }

+

+    if (decimal_point != NULL) {

+        *decimal_point = PyUnicode_DecodeLocale(lc->decimal_point, NULL);

+        if (*decimal_point == NULL) {

+            goto error;

+        }

+    }

+    if (thousands_sep != NULL) {

+        *thousands_sep = PyUnicode_DecodeLocale(lc->thousands_sep, NULL);

+        if (*thousands_sep == NULL) {

+            goto error;

+        }

+    }

+

+    if (grouping != NULL) {

+        *grouping = lc->grouping;

+    }

+

+    res = 0;

+

+error:

+    if (loc != NULL) {

+        setlocale(LC_CTYPE, oldloc);

+    }

+    PyMem_Free(oldloc);

+    return res;

+}

diff --git a/Python/formatter_unicode.c b/Python/formatter_unicode.c

index d2be76f1e1a..d3ef650e6ce 100644

--- a/Python/formatter_unicode.c

+++ b/Python/formatter_unicode.c

@@ -707,18 +707,11 @@ get_locale_info(enum LocaleType type, LocaleInfo *locale_info)

 {

     switch (type) {

     case LT_CURRENT_LOCALE: {

-        struct lconv *locale_data = localeconv();

-        locale_info->decimal_point = PyUnicode_DecodeLocale(

-                                         locale_data->decimal_point,

-                                         NULL);

-        if (locale_info->decimal_point == NULL)

+        if (_Py_GetLocaleconvNumeric(&locale_info->decimal_point,

+                                     &locale_info->thousands_sep,

+                                     &locale_info->grouping) < 0) {

             return -1;

-        locale_info->thousands_sep = PyUnicode_DecodeLocale(

-                                         locale_data->thousands_sep,

-                                         NULL);

-        if (locale_info->thousands_sep == NULL)

-            return -1;

-        locale_info->grouping = locale_data->grouping;

+        }

         break;

     }

     case LT_DEFAULT_LOCALE: