Thank you for posting your query in Microsoft Community.
Which Build are you on currently?
As we shared in July, we have been working very hard to make Cortana available in more markets and languages. On Sep 1, we rollined out Cortana to Insiders on Windows 10 Insider Preview builds
10532+ as an optional download to Insiders in Japan and in English for Insiders in Australia and Canada. We also have an early version in English for Insiders in India, which will be updated with an improved voice later this month. With these rollouts, we
hope to learn a lot from your feedback as we continue to improve the experience and refine it for each market.
If you are on legacy build, then you can still use Cortana by changing language settings to English.
Follow the below steps and see if it helps.
* Click Start,
* Navigate Settings/> Time & language /> Region & language
* Under Country or region, change the value to United States
* Reboot your PC, click on Search box on task bar, select
Cortana settings(I.e. Gear symbol) and follow the onscreen instruction to configure Cortana.
Keep us posted for any concerns with windows, we're glad to assist you.