Migrate to modern win32/winrt API for `localemodule`

Feature or enhancement

Proposal:

AFAIK, CPython has dropped support for Windows 7 since 3.9.0, while _localemodule.c contains compatibility fix for Windows NT pre-4.0. Which flag was introduced since Windows 98.

Here I listed some modern way to get locale name in BCP-47 / RFC 1766 format, is it possible to replace the legacy hex code mapping?

• GlobalizationPreferences since Windows 10 (build 10240)
• GetUserDefaultLocaleName since Windows Vista / Windows Server 2008

import ctypes
from ctypes import wintypes
from locale import getdefaultlocale, getlocale, LC_CTYPE
import warnings

# Introduced since Windows 10, BCP-47
# depends on:
# - winrt-windows-system-userprofile
# - winrt-windows-foundation
# - winrt-windows-foundation-collections
from winrt.windows.system.userprofile import GlobalizationPreferences

warnings.filterwarnings("ignore", category=DeprecationWarning)

# Load kernel32.dll
kernel32 = ctypes.WinDLL("kernel32", use_last_error=True)

# Introduced since Windows Vista, RFC 1766
# Define GetUserDefaultLocaleName signature
# int GetUserDefaultLocaleName(LPWSTR lpLocaleName, int cchLocaleName);
kernel32.GetUserDefaultLocaleName.argtypes = [wintypes.LPWSTR, ctypes.c_int]
kernel32.GetUserDefaultLocaleName.restype = ctypes.c_int

# Allocate buffer for locale name
LOCALE_NAME_MAX_LENGTH = 85  # per Windows docs


def user_default_locale() -> str:
    """
    Get user default locale encoded in BCP-47.
    """
    buffer = ctypes.create_unicode_buffer(LOCALE_NAME_MAX_LENGTH)

    # Call the function
    result = kernel32.GetUserDefaultLocaleName(buffer, LOCALE_NAME_MAX_LENGTH)

    if result == 0:
        # Call failed
        error_code = ctypes.get_last_error()
        raise ctypes.WinError(error_code)

    return buffer.value


def bcp47():
    return GlobalizationPreferences.languages[0]

>>> getdefaultlocale()
('zh_CN', 'cp936')
>>> getlocale(LC_CTYPE)
('Chinese (Simplified)_China', '936')
>>> user_default_locale()
'zh-CN'
>>> bcp47()
'zh-Hans-CN'

Has this already been discussed elsewhere?

Yes

Links to previous discussion of this feature:

gh-90817 gh-130796 https://github.com/python/cpython/issues/123853#issuecomment-3132027944

Beginne mit Modules/_localemodule.c, insbesondere mit der Kompatibilitätszuordnung für Windows NT pre-4.0. Sieh dir die verknüpften Diskussionen in gh-90817, gh-130796 und issue 123853 an und vergleiche anschließend GetUserDefaultLocaleName mit GlobalizationPreferences. Die Arbeit ist erst abgeschlossen, wenn sich das Projekt auf eine moderne API geeinigt hat und die Zuordnung der alten Hex-Codes konsistent ersetzt wurde.