I solved this problem using AutoHotKey.
Set up 3 languages, a hotkey for switching between them and another hotkey for switching to the language you want to skip. I had English, Russian and Japanese and wanted to skip Japanese so I assigned Ctrl+Shift+0 to switch to JP.
I already had an AutoHotKey script that allowed me to switch between all the 3 languages using Caps. It looked like this:
CapsLock::Send, {Alt Down}{Shift Down}{Shift Up}{Alt Up}
The idea is to switch the language automatically once you switched to the language you want to skip. It's 0x0411 for Japanese. Paste yours in the if clause in the script below, save it and run it.
Here is the list of language ids, find yours in the first column.
The script only works for switching between languages using CapsLock but you can adapt it to Alt+Shift switch. Probably just by replacing "CapsLock" with "{Alt Down}{Shift Down}{Shift Up}{Alt Up}".
CapsLock::
Send, {Alt Down}{Shift Down}{Shift Up}{Alt Up}
if !LangID := GetKeyboardLanguage(WinActive("A"))
{
MsgBox, % "GetKeyboardLayout function failed " ErrorLevel
return
}
if (LangID = 0x0411)
Send, {Alt Down}{Shift Down}{Shift Up}{Alt Up}
return
GetKeyboardLanguage(_hWnd=0)
{
if !_hWnd
ThreadId=0
else
if !ThreadId := DllCall("user32.dll\GetWindowThreadProcessId", "Ptr", _hWnd, "UInt", 0, "UInt")
return false
if !KBLayout := DllCall("user32.dll\GetKeyboardLayout", "UInt", ThreadId, "UInt")
return false
return KBLayout & 0xFFFF
}
Best Answer
Note that this isn't exactly what the OP asked for. It will work for the intended purpose (of not having to deal with the Alt + Shift cycling combination) by instead having 3 different and separate combinations for each layout.
I'm using by reference what is written here in this 7tutorials post, mainly because it has accurate and explicit screenshots.
An important note though: the last steps refer only to changing the combination that deals with the keyboard layout switch. Selecting whatever keyboard layout you want (in your case, the Japanese IME) and then pressing "Change Key Sequence" will show a different window than the one presented. You can choose to combine Left Alt + Shift + a number between 0 and 9, for instance. As such, you could have the following setup: