Paying for Speeku
One purchase per course, no subscription, and installing again for free.
Pay once
You buy each course once in the app store, and then it is yours. There is no subscription, no ads and nothing more to pay inside the app. You can see the current price on the course's store page: Speeku European Portuguese on Google Play.
One app per course
Each course is its own app, bought on its own, so you only pay for the language you are learning.
Installing again
Install the app again with the same Google account (or Apple ID) you bought it with, and the store lets you download it at no charge. On Google Play, open the course's store page and tap Install; your past purchases are also listed under Manage apps & device in the Play Store. Your progress starts fresh, because it was stored on the old phone.