Get keyboard layout on Gecko-based browsers, Windows-only

getKeyboardLayout.js

// Based on code from TabLang extension: https://addons.mozilla.org/addon/tablang/
// and Master Password+ extension https://addons.mozilla.org/addon/master-password/

var kb = {
	GetKeyboardLayout: null,
	GetLocaleInfoW: null,
	init: function()
	{
		this.init = function() {};
		Components.utils.import("resource://gre/modules/ctypes.jsm", this);
		let ctypes = this.ctypes;
		let a = Cc["@mozilla.org/xre/app-info;1"].getService(Ci.nsIXULRuntime);
		let abi = a.XPCOMABI.indexOf("x86_64") == -1 ? ctypes.winapi_abi : ctypes.default_abi;
		this.GetKeyboardLayout = ctypes.open("user32.dll").declare("GetKeyboardLayout", abi, ctypes.uintptr_t, ctypes.uint32_t);
		this.GetLocaleInfoW = ctypes.open("kernel32.dll").declare("GetLocaleInfoW", abi, ctypes.int32_t, ctypes.uint32_t, ctypes.uint32_t, ctypes.jschar.ptr, ctypes.int32_t);
	},
	getLangNameAbr: function()
	{
		this.init();
		try
		{
			let ctypes = this.ctypes;
			let lcid = ctypes.UInt64.lo(ctypes.UInt64("0x" + this.GetKeyboardLayout(0).toString(16))) & 0xFFFF;
			let bufferLength = this.GetLocaleInfoW(lcid, 89, ctypes.jschar.ptr(0), 0);
			if (bufferLength == 0)
				return;

			let buffer = ctypes.jschar.array(bufferLength)();
			if (this.GetLocaleInfoW(lcid, 89, ctypes.cast(buffer.address(), ctypes.jschar.ptr), bufferLength) != 0)
				return buffer.readString();
		}
		catch(e){};
	}
};

alert(kb.getLangNameAbr());