Apple has this great way to type non-ASCII characters like Ö or ß or € on both MacOS and iOS. You long-press the key that looks similar to what you want (an O, or an S, or a $) and then wait a bit and a UI pops up and you choose what you want from a UI picker. It’s not great for fast touch typing but for that you’d want a full language keyboard. But for wanting to type the occasional non-English word, it’s great.
Windows, not so much. The frequent advice is type it by character code as if I’m going to memorize 153 and 128 and 223. Not to mention my laptop doesn’t have a numeric keypad. The advice to use the Character Map in that post is not so awful, it works OK, but it’s pretty clumsy.
The best bet seems to be the US international keyboard. It’s an alternate American keyboard where ‘ ” ` ~ ^ are dead keys; they’ll modify the next letter to be accented, or else insert themselves if that makes no sense. It works pretty well. Even better the right Alt key can be used to type a bunch of other stuff like ß or €. It’s not perfect but it’s pretty good. Note the Windows 10 anniversary edition moved this; it’s now listed as an “Option” on the English (US) keyboard, not a separate keyboard.
I also tried Holdkey which promises to add an Apple-like typing UI. But it didn’t work very well, the way it grabs onto the keyboard is problematic. There’s some other options along these lines I didn’t try.
Update: if I type y’all I get yáll which I think is hilarious.
Update 2: by default Ctrl-Shift switches between keyboard layouts. That’s obnoxiously easy to press by accident. You can turn that off or change the key mapping.