I have had similar issues for quite a long time. I am in the UK where my best compromise is to set language to UK and keyboard to US, switching briefly to UK KB when I want the £ sign. But Shift Alt has no effect for me. Here is another quick way to switch between languages on my KB. Just to the left of the time and date at bottom right is a notification of your primary language and your keyboard, so in miy cast it is ENG US. If you press Windows Key and Space together you get a list of all the languages / Boards currently available on your system (you can add more in Settings).Hoding down the Windows Key while taping Space cycles through them, while lifting your finger from the Windows Key selects the highlighted combination, such as ENG UK. This only takes about a second to do, and to reverse it.
It is possible to opt for UK English combined with UK KB but it upsets several of my keys, such as @, ", \.. Another slight annoyance is that after a restart my KB automatically reverts to UK, so I start most sessions by selecting the US KB in the way discribed above.