您可以使用bcp47langs.dll中未记录的GetUserLanguages API，该API自Windows 8起可用。

#include <hstring.h>
#include <winstring.h>

typedef int (WINAPI* GetUserLanguagesFn)(char Delimiter, HSTRING* UserLanguages);

int main()
{
    auto h = LoadLibrary(L"bcp47langs.dll");
    auto fn = (GetUserLanguagesFn)GetProcAddress(h, "GetUserLanguages");
    HSTRING str;
    fn(',', &str);
    WindowsDeleteString(str);
    return 0;
}

public static void Main(string[] args)
{
    GetUserLanguages(',', out var langs);
    Console.WriteLine(langs);
}

[DllImport("bcp47langs")]
private static extern int GetUserLanguages(char Delimiter, [MarshalAs(UnmanagedType.HString)] out string UserLanguages);

PS：也有GetUserLanguageInputMethods存在，可以获得一种语言的输入法列表：

[DllImport("bcp47langs")]
public static extern int GetUserLanguageInputMethods(string Language, char Delimiter, [MarshalAs(UnmanagedType.HString)] out string InputMethods);

键盘布局的字符串格式：
<LangID>:<KLID>
文本服务的字符串格式为：
<LangID>:{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}
代表"西蒙·穆里尔"摆姿势。