How can I switch between language input sources using Alt-Shift on Catalina?

Question

I tried a couple of Karabiner scripts available online, but none is working.

Also, it looks like there is some confusion about what is Alt on mac keyboards. Although semantically, this is the ⌥ key, ⌘ key is positioned where Alt is on Windows keyboards.

So I would rephrase the question:

-- How can I switch between language input sources using ⌘+Shift on Catalina?

Answer 1

Punto Switcher works. Unfortunately, its main job is automagically converting Russian to English and back, and the UI is, AFAICS, only in Russian.

Still, it can map Cmd+Shift to input source switcher.