I tried to do what the instructions say here: https://github.com/rhdunn/espeak#android But as I am in Win10, and use Android Studio 2.3, don't know how to do these things in Windows? (Isn't there any step-by-step instructions for windows?)
Building with Gradle
Set the location of the Android SDK:
$ export ANDROID_HOME=<path-to-the-android-sdk>
Build the project:
$ ./autogen.sh
$ ./configure --with-gradle=<path-to-gradle>
$ make apk-release
This will create an android/build/outputs/apk/espeak-release-unsigned.apk file.