I have a weird setup, which is my fault I guess, but it results in me having two keyboards with different languages. And I frequently switch between them in my workflow, so it can be super annoying to manually switch the language every time.
On X I use a combination of two tools to automatically set the language per keyboard, which works even when hotplugging.
On wayland I found no alternative so far, but if you have any ideas, please let me know.
I don't know about other compositors, but on Hyprland and Sway you can configure things per device (in the config file). I'd give an example here but I'm on my phone right now.
I have a laptop and a desktop with slightly different keyboard layouts, and both machines share the same config file.
Not sure why you have a tool to "set the language", what would happen if you tried to use both keyboards at once?
I honestly don't recall the details and can't check right now. It's been working like that for years.
I remember the main issues I was having were around yubikey, my usb hub which can switch between two pc's and hotplugging. So I had to use a second tool which did something on any device plugin.
I think using both keyboards at once worked fine. I didn't mean system keyboard language.