HRESULT XPackageGetUserLocale(
    size_t localeSize,
    char* locale
)  

char gameLocale[LOCALE_NAME_MAX_LENGTH];

// Get the best user locale that is installed
HRESULT hr = XPackageGetUserLocale(_countof(gameLocale), gameLocale);
if (SUCCEEDED(hr))
{
    printf("Game using locale: %s\n", gameLocale);
}