First, I wanna be clear on the subject - this is a solution for all these people, who wants to use the same kbd switching shortcut as it was in Windows - perhaps - dual-OS users, or newly "baptized" Linux fellows
Second - There ALWAYS has been possibility to use Alt-Shift to switching from default keyboard layout (US English) to any other/others available! The only problem is, that we need some preparation here
So, let's get started. Open KDE Control Center (KCC) -> Keyboard Layout -> Xkb Options -> Check "Enable xkb options", then check "Group Shift/Lock behavior" -> Alt+Shift changes group". You may also find useful, if you check "ScrollLock LED shows alternative group" and "Shift with numpad keys works as in MS Windows"
That's all for this tab, now, open Keyboard Shortcuts -> Shortcut Schemes and navigate down to "Switch to Next Keyboard Layout". Then, you have to select desired shortcut - PRESS Alt+Shift and that's ALL! After selecting this, you'll see "Alt+ISO_Prev_Group" - this it your newly selected kbd switching shortcut - Alt+Shift
Now, return to "Keyboard layout" -> "Layout" Tab and REMOVE from the list of installed kbd layouts US English, leave there ONLY your country keyboard layout BUT - be sure, to check "Include latin layout" !!! - this is the way, to have native English, along with your language available. Apply all these settings and you are done!
Well, not quite
Try to switch your keyboard - you'll see, that keyboard layout actually changes, ScrollLock LED lights, when you switch to alternate layout BUT - KDE Keyboard Indicator (Kxkb) does not change it's state! There always will be American flag, even you are writing in your native language. This, and only this has been the problem for a long time ago.
So, if you're comfortable with this side effect - congratulations
If you're not - continue reading
There is a little application, called Kkbswitch - go and install it via Synaptic
then start it (Alt+F2, kkbswitch) and you'll see something familiar
Try to configure it - surprisingly, it has the same visual output as the original KDE Indicator - country flags with two-letters country code! Any time, when you press Alt-Shift, it's indicator changes to proper flag/code, but not KDE Indicator... So - you do not need KDE Indicator anymore. Go to KCC -> Keyboard Layout -> "Switching Options" and UNCHECK obsolete "Show indicator for single layout" and "Show country flag".
That's all folks! Hope it's all been clear, but here is some screenshots, that may help
p.s. Sorry for my bad english, I'm from Bulgaria, as you may see