How to choose a "sound" source of the video in Cubase 10 Pro?

Hello.

I’ve got a film with 2 “inbuilt” audio sources (russian and original language). In VLC I can switch between them. How can I switch between them in Cubase?

In some reason Cubase 10 Pro won’t import file of AVI extension. Why?

Thanks

Because it’s not supported. There is a list of files on the steinberg site that lists supported formats. You will have to convert it so Cubase can read it.