diff --git a/CHANGES b/CHANGES
index fcbbdb43295..9d3edcb8969 100644
--- a/CHANGES
+++ b/CHANGES
@@ -15,6 +15,8 @@ Incompatible changes
   ``setup.py``).
 * #11364: Remove deprecated ``sphinx.ext.napoleon.iterators`` module.
 * #11365: Remove support for the ``jsdump`` format in ``sphinx.search``.
+* #11366: Make ``locale`` a required argument to
+  ``sphinx.util.i18n.format_date()``.
 
 Deprecated
 ----------
diff --git a/sphinx/util/i18n.py b/sphinx/util/i18n.py
index 3069b5458f9..268633200ad 100644
--- a/sphinx/util/i18n.py
+++ b/sphinx/util/i18n.py
@@ -4,7 +4,6 @@
 
 import os
 import re
-import warnings
 from datetime import datetime, timezone
 from os import path
 from typing import TYPE_CHECKING, Callable, Generator, NamedTuple
@@ -13,7 +12,6 @@
 from babel.messages.mofile import write_mo
 from babel.messages.pofile import read_po
 
-from sphinx.deprecation import RemovedInSphinx70Warning
 from sphinx.errors import SphinxError
 from sphinx.locale import __
 from sphinx.util import logging
@@ -171,11 +169,6 @@ def docname_to_domain(docname: str, compaction: bool | str) -> str:
 
 def babel_format_date(date: datetime, format: str, locale: str,
                       formatter: Callable = babel.dates.format_date) -> str:
-    if locale is None:
-        warnings.warn('The locale argument for babel_format_date() becomes required.',
-                      RemovedInSphinx70Warning)
-        locale = 'en'
-
     # Check if we have the tzinfo attribute. If not we cannot do any time
     # related formats.
     if not hasattr(date, 'tzinfo'):
@@ -193,7 +186,7 @@ def babel_format_date(date: datetime, format: str, locale: str,
 
 
 def format_date(
-    format: str, date: datetime | None = None, language: str | None = None,
+    format: str, *, date: datetime | None = None, language: str,
 ) -> str:
     if date is None:
         # If time is not specified, try to use $SOURCE_DATE_EPOCH variable
@@ -204,11 +197,6 @@ def format_date(
         else:
             date = datetime.now(timezone.utc).astimezone()
 
-    if language is None:
-        warnings.warn('The language argument for format_date() becomes required.',
-                      RemovedInSphinx70Warning)
-        language = 'en'
-
     result = []
     tokens = date_format_re.split(format)
     for token in tokens:
diff --git a/tests/test_util_i18n.py b/tests/test_util_i18n.py
index 7be6f3e779a..8aae9402847 100644
--- a/tests/test_util_i18n.py
+++ b/tests/test_util_i18n.py
@@ -2,7 +2,6 @@
 
 import datetime
 import os
-import warnings
 
 import babel
 import pytest
@@ -57,11 +56,6 @@ def test_format_date():
 
     # strftime format
     format = '%B %d, %Y'
-    with warnings.catch_warnings():
-        # Test format_date() with no language argument -- this form will be
-        # removed in Sphinx 7 (xref RemovedInSphinx70Warning)
-        warnings.simplefilter("ignore")
-        assert i18n.format_date(format, date=date) == 'February 07, 2016'
     assert i18n.format_date(format, date=date, language='') == 'February 07, 2016'
     assert i18n.format_date(format, date=date, language='unknown') == 'February 07, 2016'
     assert i18n.format_date(format, date=date, language='en') == 'February 07, 2016'