Script for http://superuser.com/questions/429930 (.ahk)

#NoEnv
#SingleInstance force

$~CapsLock::LangSwitch(1)
$~CapsLock up::LangSwitch(2)

LangSwitch( iKeyDownUp=0 )
{
    static tickLast
    IfEqual,iKeyDownUp,1
    {   tickLast=%A_TickCount%
        return
    }
    IfEqual,iKeyDownUp,2
        If( A_TickCount-tickLast>200 )
            return

    HKL:=DllCall("GetKeyboardLayout", "uint",GetThreadOfWindow(), "uint")

    HKLnum:=DllCall("GetKeyboardLayoutList","uint",0,"uint",0)
    VarSetCapacity( HKLlist, HKLnum*4, 0 )
    DllCall("GetKeyboardLayoutList","uint",HKLnum,"uint",&HKLlist)
    loop,%HKLnum%
    {   if( NumGet( HKLlist, (A_Index-1)*4 ) = HKL )
        {   HKL:=NumGet( HKLlist, mod(A_Index,HKLnum)*4 )
            break
        }
    }
    ControlGetFocus,ctl,A
    SendMessage,0x50,0,HKL,%ctl%,A ;WM_INPUTLANGCHANGEREQUEST

    ;show traytip
    LOCALE_SENGLANGUAGE=0x1001
    LOCALE_SENGCOUNTRY=0x1002
    VarSetCapacity( sKbd, 260, 0 )
    VarSetCapacity( sCountry, 260, 0 )
    DllCall("GetLocaleInfo","uint",HKL>>16,"uint",LOCALE_SENGLANGUAGE, "str",sKbd, "uint",260)
    DllCall("GetLocaleInfo","uint",HKL & 0xFFFF,"uint",LOCALE_SENGCOUNTRY, "str",sCountry, "uint",260)
    traytip,%sKbd%,%sCountry%
    SetTimer,REMOVE_TOOLTIP,500 ;0.5 second
    return
REMOVE_TOOLTIP:
    SetTimer,REMOVE_TOOLTIP,off
    traytip
    return
}

;returns first thread for the <processID>
;sets optional <List> to pipe | separated thread list for the <processID>
GetProcessThreadOrList( processID, byRef list="" )
{
    ;THREADENTRY32 {
    THREADENTRY32_dwSize=0 ; DWORD
    THREADENTRY32_cntUsage = 4  ;DWORD
    THREADENTRY32_th32ThreadID = 8  ;DWORD
    THREADENTRY32_th32OwnerProcessID = 12   ;DWORD
    THREADENTRY32_tpBasePri = 16    ;LONG
    THREADENTRY32_tpDeltaPri = 20   ;LONG
    THREADENTRY32_dwFlags = 24  ;DWORD
    THREADENTRY32_SIZEOF = 28

    TH32CS_SNAPTHREAD=4

    hProcessSnap := DllCall("CreateToolhelp32Snapshot","uint",TH32CS_SNAPTHREAD, "uint",0)
    ifEqual,hProcessSnap,-1, return

    VarSetCapacity( thE, THREADENTRY32_SIZEOF, 0 )
    NumPut( THREADENTRY32_SIZEOF, thE )

    ret=-1

    if( DllCall("Thread32First","uint",hProcessSnap, "uint",&thE ))
        loop
        {
            if( NumGet( thE ) >= THREADENTRY32_th32OwnerProcessID + 4)
                if( NumGet( thE, THREADENTRY32_th32OwnerProcessID ) = processID )
                {   th := NumGet( thE, THREADENTRY32_th32ThreadID )
                    IfEqual,ret,-1
                        ret:=th
                    list .=  th "|"
                }
            NumPut( THREADENTRY32_SIZEOF, thE )
            if( DllCall("Thread32Next","uint",hProcessSnap, "uint",&thE )=0)
                break
        }

    DllCall("CloseHandle","uint",hProcessSnap)
    StringTrimRight,list,list,1
    return ret
}

; Returns thread owning specified window handle
; default = Active window
GetThreadOfWindow( hWnd=0 )
{
    IfEqual,hWnd,0
        hWnd:=WinExist("A")
    DllCall("GetWindowThreadProcessId", "uint",hWnd, "uintp",id)
    GetProcessThreadOrList(  id, threads )
    IfEqual,threads,
        return 0
    CB:=RegisterCallback("GetThreadOfWindowCallBack","Fast")
    lRet=0
    lParam:=hWnd
    loop,parse,threads,|
    {   NumPut( hWnd, lParam )
        DllCall("EnumThreadWindows", "uint",A_LoopField, "uint",CB, "uint",&lParam)
        if( NumGet( lParam )=true )
        {   lRet:=A_LoopField
            break
        }
    }
    DllCall("GlobalFree", "uint", CB)
    return lRet
}

GetThreadOfWindowCallBack( hWnd, lParam )
{
    IfNotEqual,hWnd,% NumGet( 0+lParam )
        return true
    NumPut( true, 0+lParam )
    return 0
}