How to Enable Cortana on Windows 10 in Ireland, and other non-US locations [UPDATED with Universal A
As with Windows Phone, when Cortana was first released she was only available for the United States and not available in the rest of the world. However, through some easy configuration shenanigans many were able to use Cortana outside of the United States.
It's a similar story with Cortana on Windows 10. In the latest Technical Preview build (9926) Microsoft have enabled Cortana only for the United States. Through some configuration settings, we have been able to switch on the feature in Ireland and the same steps should work for all non-US locations.
How to enable Cortana outside of the US.
1. Right click on the Start button and select Control Panel
2. Select Clock, Language and Region
3. Select Change Location
4. Set Home Location to United States, then click OK
5. Select Language.
6. Click Add a Language, and add English (United States) as move to the top of the list, as your preferred language.
Note: You may need to click Options and Download and install language pack to complete the process.
After you have completed this, when you click on the Search box or the search icon Cortana will now ask you what you want to be called and prompt you to complete the initial configuration.
Please note that Cortana in build 9926 is very early work in progress and is not as feature rich as her Phone counterpart, but Microsoft will definitely work to improve her over the coming builds.
[UPDATE 26 Jan 2015, 14:07]
Thanks to all who have pointed out the steps using the newer Settings, Universal App
1. Click Start, then select Settings
2. Select Time & Language
3. From here, select your Country as United States and add the language English (United States)