[Χάρης Καραχριστιανίδης]

I followed this guide http://awesome.naquadah.org/wiki/Change_keyboard_maps and
pasted

-- Keyboard map indicator and changer
kbdcfg = {}
kbdcfg.cmd = "setxkbmap"
kbdcfg.layout = { { "us", "" }, { "gr", "" } }
kbdcfg.current = 1  -- us is our default layout
kbdcfg.widget = wibox.widget.textbox()
kbdcfg.widget:set_text(" " .. kbdcfg.layout[kbdcfg.current][1] .. " ")
kbdcfg.switch = function ()
  kbdcfg.current = kbdcfg.current % #(kbdcfg.layout) + 1
  local t = kbdcfg.layout[kbdcfg.current]
  kbdcfg.widget:set_text(" " .. t[1] .. " ")
  os.execute( kbdcfg.cmd .. " " .. t[1] .. " " .. t[2] )
end

 -- Mouse bindings
kbdcfg.widget:buttons(
 awful.util.table.join(awful.button({ }, 1, function () kbdcfg.switch() end))
)

and

-- Alt + Right Shift switches the current keyboard layout
    awful.key({ "Mod1" }, "Shift_R", function () kbdcfg.switch() end),