It doesn't? I'm multilingual and always had 3 keyboard languages in parallel and never had any of those issues happen in 15+ years and 6 versions of Windows.
Most likely he was hitting alt+space by accident which cycles through them without him realizing.
Hot take: I feel like a lot of Windows issues people raise are actually user errors/accidents, then blaming the OS for it.
Could be ctrl+shift. It's easy to mistype, and there's no UI feedback. Also used to only change a single window's language (not sure if that's the case anymore, as I use win+space).
If enough people are unaware that they're telling the software to do something and are confused by its behavior, then the software needs to better indicate what it's doing and why.
And who gets to be the judge of which keybinds are "random and mysterious"? Every single OS has it's own different keybinds you need to learn if you want to be eficient with. MacOS has different. KDE has different. Gnome has different. Windows has different. It's not their fault you don't know them or haven't bothered to look into them for the OS you daily drive at home or at work and remain "random and mysterious" to you. Every switch to a new OS involves a certain learning curve for any user.
It's called basic computer literacy in my country and it's also must have knowledge for most white collar jobs as it's part of the curriculum out of high-school.
If you don't have the basic skills to Google "hotkey keyboard layout switch Windows" or something along those lines for your OS, then "you'd better get used to asking people if they want fries with their order", as our instructor used to say, since you're not getting into any tech career if you can't google basic stuff.
> that nobody asked for
As a multilingual person who has to type in 3 languages on daily basis, the keybinds to quickly switch languages are defiantly something I would have asked for and I'm glad they exist.
I know the keybind to switch languages. I'm ok with it. I'm genuinely asking why Windows is adamant that I must have more keyboard language options than the two very specific ones I want.
Most likely he was hitting alt+space by accident which cycles through them without him realizing.
Hot take: I feel like a lot of Windows issues people raise are actually user errors/accidents, then blaming the OS for it.