Maybe sometimes, but in my case using Swedish and English the thing is that a Swedish keyboard basically just adds three extra characters (å ä ö) in addition to what the English keyboard has, so I would prefer to always have a Swedish keyboard layout, there is not much point in selecting the English one. Especially since even when I write in English I might want/need to throw in a Swedish word (or a name of a Swedish person having å ä ö in the name) as part of the text I am writing in English. So I would prefer having the Swedish keyboard always. I think it might be like that for many other languages as well, that the keyboard mostly adds a few extra things in addition to what the English keyboard has.
Also, even if the computer/phone could somehow know which language I am currently typing in, there are always cases where languages mix, I use some words from the other language in the middle of the text, I want to be able to do that without switching keyboard layouts if all characters I need are anyway available in the Swedish layout, then I want to be able to write something in English while having the Swedish keyboard selected so that I can use å ä ö in the middle of my English text, it could be just for persons’ names that use those characters.
Just like the laptop I’m using to type this right now, it has the å ä ö keys on its keyboard which is good for me, and that does not stop me from writing in English, I don’t need a special English keyboard for that.