From a post I made on what was then the Windows 10 for Screen Reader Users Group, now the Windows Access with Screen Readers Group:
In Settings, Time and Language, Language Pane you can add languages with the Add Languages button. I've added English language packs for Australia, Canada, and the UK. This makes the various OneCore voices associated with those language packs available for my use, whether in Windows 10 itself or a screen reader. Make sure when you're looking at a language that it will work with Text-to-Speech if the intention is to use it with a screen reader, as not all do.
If you want to check what voices you currently have installed, it's the same Windows 10 Settings but choose the Speech Pane. The voice dropdown shows the voices currently available on your machine. You can also add languages and the voices for same in this pane as well with the Add voices button. That will open up the dialog that lets you search for languages, and dialects within certain languages, and once you've picked and installed the language packs you want the voices for those will appear in the voices dropdown.
As is typical, Microsoft gives you more than one way to accomplish the same end.
Brian - Windows 10, 64-Bit, Version 21H1, Build 19043
I do not understand why some seek to separate a person from their actions. The self is composed of an individual’s thoughts, actions, and expression, which are contained in and actuated by the body. What you do and say is the clearest indicator of who you are.
~ Brian Vogel