As part of the Insider program I get rather frequent upgrades to Windows 10. Each time the upgrade installs it resets my speech language to “English (United States)” which means Cortana stops working as my Region is set to “Australia”
I also use ConfigMgr to handle updates on my network (this would also apply for people using WSUS) so when I go into the Region & language settings I don’t get the Speech feature appearing under the “English (Australia)” options.
Luckily, it is relatively easy to sort out.