ELSA Speak application is available to be installed via Google Play Store (Android) and App Store (Apple). Depending on your country or region, you might not be able to install/use the ELSA Speak application or purchase in-app subscriptions to ELSA.
For more information on the availability of ELSA in different countries, visit the below pages.
Apple App-Store: Availability of Apple Media Services
Google Play Store Paid app availability – Google Play Help