You can restore your purchases between Android devices or iOS devices.
On Android devices you can do so only to restore your purchase of the old app in the new one and only in case of apps that feature a single language course.
On iOS you can restore your purchase of the new app that features all 34 language courses if you installed it on another device.
If you want to restore your purchases on iOS devices, you have to be signed in with the same iTunes account you used for the purchase. Then you have to:
1. Go to the "More" tab.
2. Tap on the "Restore Purchases" menu option. 
3. Tap on "Yes" when asked if you want to restore your purchases.
If you want to restore your purchases on Android devices, you have to provide the Order Number from the purchase receipt. Just follow these steps:
1. Go to the "More" tab.
2. Tap on the "Restore Purchases" menu option.
3. Enter the Order Number and tap "Restore Purchase".