well, strangely enough after posting the previous comment, I found out about bug #1260226 which tells that alt + shift and ctrl + shift still work on XOrg's side so simply you can click alt+shift to switch language while on lockscreen and it just works !!
well, strangely enough after posting the previous comment, I found out about bug #1260226 which tells that alt + shift and ctrl + shift still work on XOrg's side so simply you can click alt+shift to switch language while on lockscreen and it just works !!