Windows allows you to change your keyboard setting easily. I use the Polish keyboard for both Polish and English, and switch to the German or Danish keyboards when I have to write in those languages.
That's true, but still the descriptions on the keys are a problem. Having a laptop with an American vel Polish keyboard, when I switch to a standard German keyboard layout, I don't know where the letters with umlauts are (it's easier when someone works with a German keyboard every day and just remembers where they are, but this is not my case), not to mention that some of the special characters like _ have also changed locations. And Y and Z are exchanged, but this is the least important problem when you remember about this.
I deal with this using an "English-multilingual" layout (in Linux; in Windows, I think, it's necessary to download and install something like this, it's not present by default - but I may be mistaken), which has for example ü under Alt+Y or ö under Alt+P, so it works more or less like a Polish keyboard.