I have already described briefly what they are and how they work, but I want to repeat myself because it seems that the concept has not yet been understood.
The application is free and all of its functions can be accessed without paying anything. The access is immediate if you have credits, while you have to wait 15 seconds if you do not have. That's it.
When you install the app you start with 5000 credits and every time you access a localization function an amount between 5 to 50 credits is subtracted. Registration will cost 1000 credits, but is not mandatory.
With these values, the application can be used for several months before you run out of credits.
Credit management is automatic and the user does not have to do anything. You realize that you are out of credits when you see a 15 seconds wait screen before you access a localization function. At that point you can decide whether it is better to wait or invest a little time to get some free credits.
Each credit you get for free means for me a fraction of a penny earned ($0.0002). This is the only way you have to support the development of the application because unlike many other programmers I did not put any advertising.
I know that there are many people who prefer to buy the application. For them I'm already at work, I'll put the new version online before the end of the year.