diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -440,6 +440,7 @@
   __locale_dir/locale_base_api/bsd_locale_defaults.h
   __locale_dir/locale_base_api/bsd_locale_fallbacks.h
   __locale_dir/locale_base_api/locale_guard.h
+  __locale_dir/locale_base_api.h
   __mbstate_t.h
   __memory/addressof.h
   __memory/align.h
@@ -574,19 +575,11 @@
   __string/char_traits.h
   __string/constexpr_c_functions.h
   __string/extern_template_lists.h
-  __support/android/locale_bionic.h
-  __support/fuchsia/xlocale.h
   __support/ibm/gettod_zos.h
   __support/ibm/locale_mgmt_zos.h
   __support/ibm/nanosleep.h
-  __support/ibm/xlocale.h
-  __support/musl/xlocale.h
-  __support/newlib/xlocale.h
-  __support/openbsd/xlocale.h
   __support/solaris/floatingpoint.h
   __support/solaris/wchar.h
-  __support/solaris/xlocale.h
-  __support/win32/locale_win32.h
   __support/xlocale/__nop_locale_mgmt.h
   __support/xlocale/__posix_l_fallback.h
   __support/xlocale/__strtonum_fallback.h
diff --git a/libcxx/include/__locale b/libcxx/include/__locale
--- a/libcxx/include/__locale
+++ b/libcxx/include/__locale
@@ -12,6 +12,7 @@
 
 #include <__availability>
 #include <__config>
+#include <__locale_dir/locale_base_api.h>
 #include <cctype>
 #include <clocale>
 #include <cstdint>
@@ -26,30 +27,6 @@
 #  include <cwchar>
 #endif
 
-#if defined(_LIBCPP_MSVCRT_LIKE)
-# include <__support/win32/locale_win32.h>
-#elif defined(_AIX) || defined(__MVS__)
-# include <__support/ibm/xlocale.h>
-#elif defined(__ANDROID__)
-# include <__support/android/locale_bionic.h>
-#elif defined(__sun__)
-# include <__support/solaris/xlocale.h>
-# include <xlocale.h>
-#elif defined(_NEWLIB_VERSION)
-# include <__support/newlib/xlocale.h>
-#elif defined(__OpenBSD__)
-# include <__support/openbsd/xlocale.h>
-#elif (defined(__APPLE__) || defined(__FreeBSD__))
-# include <xlocale.h>
-#elif defined(__Fuchsia__)
-# include <__support/fuchsia/xlocale.h>
-#elif defined(__wasi__)
-// WASI libc uses musl's locales support.
-# include <__support/musl/xlocale.h>
-#elif defined(_LIBCPP_HAS_MUSL_LIBC)
-# include <__support/musl/xlocale.h>
-#endif
-
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
diff --git a/libcxx/include/__locale_dir/locale_base_api.h b/libcxx/include/__locale_dir/locale_base_api.h
new file mode 100644
--- /dev/null
+++ b/libcxx/include/__locale_dir/locale_base_api.h
@@ -0,0 +1,63 @@
+//===-----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___LOCALE_DIR_LOCALE_BASE_API_H
+#define _LIBCPP___LOCALE_DIR_LOCALE_BASE_API_H
+
+#if defined(_LIBCPP_MSVCRT_LIKE)
+#  include <__locale_dir/locale_base_api/win32.h>
+#elif defined(_AIX) || defined(__MVS__)
+#  include <__locale_dir/locale_base_api/ibm.h>
+#elif defined(__ANDROID__)
+#  include <__locale_dir/locale_base_api/android.h>
+#elif defined(__sun__)
+#  include <__locale_dir/locale_base_api/solaris.h>
+#elif defined(_NEWLIB_VERSION)
+#  include <__locale_dir/locale_base_api/newlib.h>
+#elif defined(__OpenBSD__)
+#  include <__locale_dir/locale_base_api/openbsd.h>
+#elif defined(__Fuchsia__)
+#  include <__locale_dir/locale_base_api/fuchsia.h>
+#elif defined(__wasi__) || defined(_LIBCPP_HAS_MUSL_LIBC)
+#  include <__locale_dir/locale_base_api/musl.h>
+#elif defined(__APPLE__) || defined(__FreeBSD__)
+#  include <xlocale.h>
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+/*
+The platform-specific headers have to provide the following interface:
+
+// TODO: rename this to __libcpp_locale_t
+using locale_t = //implementation-defined//;
+
+//implementation-defined// __libcpp_mb_cur_max_l(locale_t);
+wint_t __libcpp_btowc_l(int, locale_t);
+int __libcpp_wctob_l(wint_t, locale_t);
+size_t __libcpp_wcsnrtombs_l(char* dest, const wchar_t** src, size_t wide_char_count, size_t len, mbstate_t, locale_t);
+size_t __libcpp_wcrtomb_l(char* str, wchar_t wide_char, mbstate_t*, locale_t);
+size_t __libcpp_mbsnrtowcs_l(wchar_t* dest, const char** src, size_t max_out, size_t len, mbstate_t*, locale_t);
+size_t __libcpp_mbrtowc_l(wchar_t* dest, cosnt char* src, size_t count, mbstate_t*, locale_t);
+int __libcpp_mbtowc_l(wchar_t* dest, const char* src, size_t count, locale_t);
+size_t __libcpp_mbrlen_l(const char* str, size_t count, mbstate_t*, locale_t);
+lconv* __libcpp_localeconv_l(locale_t);
+size_t __libcpp_mbsrtowcs_l(wchar_t* dest, const char** src, size_t len, mbstate_t*, locale_t);
+int __libcpp_snprintf_l(char* dest, size_t buff_size, locale_t, const char* format, ...);
+int __libcpp_asprintf_l(char** dest, locale_t, const char* format, ...);
+int __libcpp_sscanf_l(const char* dest, locale_t, const char* format, ...);
+
+These functions are equivalent to their C counterparts,
+except that locale_t is used instead of the current global locale.
+
+The variadic functions may be implemented as templates with a parameter pacj instead of variadic functions
+*/
+
+#endif // _LIBCPP___LOCALE_DIR_LOCALE_BASE_API_H
diff --git a/libcxx/include/__support/android/locale_bionic.h b/libcxx/include/__locale_dir/locale_base_api/android.h
rename from libcxx/include/__support/android/locale_bionic.h
rename to libcxx/include/__locale_dir/locale_base_api/android.h
--- a/libcxx/include/__support/android/locale_bionic.h
+++ b/libcxx/include/__locale_dir/locale_base_api/android.h
@@ -7,8 +7,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef _LIBCPP___SUPPORT_ANDROID_LOCALE_BIONIC_H
-#define _LIBCPP___SUPPORT_ANDROID_LOCALE_BIONIC_H
+#ifndef _LIBCPP___LOCALE_LOCALE_BASE_API_ANDROID_H
+#define _LIBCPP___LOCALE_LOCALE_BASE_API_ANDROID_H
 
 #if defined(__BIONIC__)
 
@@ -69,4 +69,4 @@
 #endif // defined(__ANDROID__)
 
 #endif // defined(__BIONIC__)
-#endif // _LIBCPP___SUPPORT_ANDROID_LOCALE_BIONIC_H
+#endif // _LIBCPP___LOCALE_LOCALE_BASE_API_ANDROID_H
diff --git a/libcxx/include/__support/fuchsia/xlocale.h b/libcxx/include/__locale_dir/locale_base_api/fuchsia.h
rename from libcxx/include/__support/fuchsia/xlocale.h
rename to libcxx/include/__locale_dir/locale_base_api/fuchsia.h
--- a/libcxx/include/__support/fuchsia/xlocale.h
+++ b/libcxx/include/__locale_dir/locale_base_api/fuchsia.h
@@ -7,8 +7,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef _LIBCPP___SUPPORT_FUCHSIA_XLOCALE_H
-#define _LIBCPP___SUPPORT_FUCHSIA_XLOCALE_H
+#ifndef _LIBCPP___LOCALE_LOCALE_BASE_API_FUCHSIA_H
+#define _LIBCPP___LOCALE_LOCALE_BASE_API_FUCHSIA_H
 
 #if defined(__Fuchsia__)
 
@@ -19,4 +19,4 @@
 
 #endif // defined(__Fuchsia__)
 
-#endif // _LIBCPP___SUPPORT_FUCHSIA_XLOCALE_H
+#endif // _LIBCPP___LOCALE_LOCALE_BASE_API_FUCHSIA_H
diff --git a/libcxx/include/__support/ibm/xlocale.h b/libcxx/include/__locale_dir/locale_base_api/ibm.h
rename from libcxx/include/__support/ibm/xlocale.h
rename to libcxx/include/__locale_dir/locale_base_api/ibm.h
--- a/libcxx/include/__support/ibm/xlocale.h
+++ b/libcxx/include/__locale_dir/locale_base_api/ibm.h
@@ -7,8 +7,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef _LIBCPP___SUPPORT_IBM_XLOCALE_H
-#define _LIBCPP___SUPPORT_IBM_XLOCALE_H
+#ifndef _LIBCPP___LOCALE_LOCALE_BASE_API_IBM_H
+#define _LIBCPP___LOCALE_LOCALE_BASE_API_IBM_H
 
 #if defined(__MVS__)
 #include <__support/ibm/locale_mgmt_zos.h>
@@ -126,4 +126,4 @@
 #ifdef __cplusplus
 }
 #endif
-#endif // _LIBCPP___SUPPORT_IBM_XLOCALE_H
+#endif // _LIBCPP___LOCALE_LOCALE_BASE_API_IBM_H
diff --git a/libcxx/include/__support/musl/xlocale.h b/libcxx/include/__locale_dir/locale_base_api/musl.h
rename from libcxx/include/__support/musl/xlocale.h
rename to libcxx/include/__locale_dir/locale_base_api/musl.h
--- a/libcxx/include/__support/musl/xlocale.h
+++ b/libcxx/include/__locale_dir/locale_base_api/musl.h
@@ -14,8 +14,8 @@
 // in Musl.
 //===----------------------------------------------------------------------===//
 
-#ifndef _LIBCPP___SUPPORT_MUSL_XLOCALE_H
-#define _LIBCPP___SUPPORT_MUSL_XLOCALE_H
+#ifndef _LIBCPP___LOCALE_LOCALE_BASE_API_MUSL_H
+#define _LIBCPP___LOCALE_LOCALE_BASE_API_MUSL_H
 
 #include <cstdlib>
 #include <cwchar>
@@ -49,4 +49,4 @@
 }
 #endif
 
-#endif // _LIBCPP___SUPPORT_MUSL_XLOCALE_H
+#endif // _LIBCPP___LOCALE_LOCALE_BASE_API_MUSL_H
diff --git a/libcxx/include/__support/newlib/xlocale.h b/libcxx/include/__locale_dir/locale_base_api/newlib.h
rename from libcxx/include/__support/newlib/xlocale.h
rename to libcxx/include/__locale_dir/locale_base_api/newlib.h
--- a/libcxx/include/__support/newlib/xlocale.h
+++ b/libcxx/include/__locale_dir/locale_base_api/newlib.h
@@ -6,8 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef _LIBCPP___SUPPORT_NEWLIB_XLOCALE_H
-#define _LIBCPP___SUPPORT_NEWLIB_XLOCALE_H
+#ifndef _LIBCPP___LOCALE_LOCALE_BASE_API_NEWLIB_H
+#define _LIBCPP___LOCALE_LOCALE_BASE_API_NEWLIB_H
 
 #if defined(_NEWLIB_VERSION)
 
@@ -20,4 +20,4 @@
 
 #endif // _NEWLIB_VERSION
 
-#endif
+#endif // _LIBCPP___LOCALE_LOCALE_BASE_API_NEWLIB_H
diff --git a/libcxx/include/__support/openbsd/xlocale.h b/libcxx/include/__locale_dir/locale_base_api/openbsd.h
rename from libcxx/include/__support/openbsd/xlocale.h
rename to libcxx/include/__locale_dir/locale_base_api/openbsd.h
--- a/libcxx/include/__support/openbsd/xlocale.h
+++ b/libcxx/include/__locale_dir/locale_base_api/openbsd.h
@@ -7,8 +7,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef _LIBCPP___SUPPORT_OPENBSD_XLOCALE_H
-#define _LIBCPP___SUPPORT_OPENBSD_XLOCALE_H
+#ifndef _LIBCPP___LOCALE_LOCALE_BASE_API_OPENBSD_H
+#define _LIBCPP___LOCALE_LOCALE_BASE_API_OPENBSD_H
 
 #include <__support/xlocale/__strtonum_fallback.h>
 #include <clocale>
@@ -32,4 +32,4 @@
 }
 #endif
 
-#endif
+#endif // _LIBCPP___LOCALE_LOCALE_BASE_API_OPENBSD_H
diff --git a/libcxx/include/__support/solaris/xlocale.h b/libcxx/include/__locale_dir/locale_base_api/solaris.h
rename from libcxx/include/__support/solaris/xlocale.h
rename to libcxx/include/__locale_dir/locale_base_api/solaris.h
--- a/libcxx/include/__support/solaris/xlocale.h
+++ b/libcxx/include/__locale_dir/locale_base_api/solaris.h
@@ -10,8 +10,8 @@
 // Minimal xlocale implementation for Solaris.  This implements the subset of
 // the xlocale APIs that libc++ depends on.
 ////////////////////////////////////////////////////////////////////////////////
-#ifndef __XLOCALE_H_INCLUDED
-#define __XLOCALE_H_INCLUDED
+#ifndef _LIBCPP___LOCALE_LOCALE_BASE_API_SOLARIS_H
+#define _LIBCPP___LOCALE_LOCALE_BASE_API_SOLARIS_H
 
 #include <stdlib.h>
 
@@ -72,4 +72,4 @@
 }
 #endif
 
-#endif
+#endif // _LIBCPP___LOCALE_LOCALE_BASE_API_SOLARIS_H
diff --git a/libcxx/include/__support/win32/locale_win32.h b/libcxx/include/__locale_dir/locale_base_api/win32.h
rename from libcxx/include/__support/win32/locale_win32.h
rename to libcxx/include/__locale_dir/locale_base_api/win32.h
--- a/libcxx/include/__support/win32/locale_win32.h
+++ b/libcxx/include/__locale_dir/locale_base_api/win32.h
@@ -7,8 +7,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef _LIBCPP___SUPPORT_WIN32_LOCALE_WIN32_H
-#define _LIBCPP___SUPPORT_WIN32_LOCALE_WIN32_H
+#ifndef _LIBCPP___LOCALE_LOCALE_BASE_API_WIN32_H
+#define _LIBCPP___LOCALE_LOCALE_BASE_API_WIN32_H
 
 #include <__config>
 #include <cstddef>
@@ -279,4 +279,4 @@
     return ( __c == L' ' || __c == L'\t' );
 }
 
-#endif // _LIBCPP___SUPPORT_WIN32_LOCALE_WIN32_H
+#endif // _LIBCPP___LOCALE_LOCALE_BASE_API_WIN32_H
diff --git a/libcxx/include/module.modulemap.in b/libcxx/include/module.modulemap.in
--- a/libcxx/include/module.modulemap.in
+++ b/libcxx/include/module.modulemap.in
@@ -1112,6 +1112,10 @@
     @requires_LIBCXX_ENABLE_LOCALIZATION@
     header "locale"
     export *
+
+    module __locale {
+      module locale_base_api { private header "__locale_dir/locale_base_api.h" }
+    }
   }
   module map {
     header "map"
diff --git a/libcxx/utils/data/ignore_format.txt b/libcxx/utils/data/ignore_format.txt
--- a/libcxx/utils/data/ignore_format.txt
+++ b/libcxx/utils/data/ignore_format.txt
@@ -455,9 +455,15 @@
 libcxx/include/list
 libcxx/include/__locale
 libcxx/include/locale
+libcxx/include/__locale_dir/locale_base_api/android.h
 libcxx/include/__locale_dir/locale_base_api/bsd_locale_defaults.h
 libcxx/include/__locale_dir/locale_base_api/bsd_locale_fallbacks.h
+libcxx/include/__locale_dir/locale_base_api/fuchsia.h
+libcxx/include/__locale_dir/locale_base_api/ibm.h
 libcxx/include/__locale_dir/locale_base_api/locale_guard.h
+libcxx/include/__locale_dir/locale_base_api/newlib.h
+libcxx/include/__locale_dir/locale_base_api/solaris.h
+libcxx/include/__locale_dir/locale_base_api/win32.h
 libcxx/include/locale.h
 libcxx/include/map
 libcxx/include/math.h
@@ -602,15 +608,9 @@
 libcxx/include/string.h
 libcxx/include/string_view
 libcxx/include/strstream
-libcxx/include/__support/android/locale_bionic.h
-libcxx/include/__support/fuchsia/xlocale.h
 libcxx/include/__support/ibm/gettod_zos.h
 libcxx/include/__support/ibm/locale_mgmt_zos.h
 libcxx/include/__support/ibm/nanosleep.h
-libcxx/include/__support/ibm/xlocale.h
-libcxx/include/__support/newlib/xlocale.h
-libcxx/include/__support/solaris/xlocale.h
-libcxx/include/__support/win32/locale_win32.h
 libcxx/include/__support/xlocale/__nop_locale_mgmt.h
 libcxx/include/system_error
 libcxx/include/thread