I tried the free "base version" to check whether the program might assist me to learn a new language. While I like the general appearance and features, I could not work with the free version at all. There is NO way to remove downloaded word sets - many of which are faulty, e.g. because they have the languages mixed up (e.g. words in the "english" column while it should be in the column of the foreign language) and you only understand this after it is downloaded. You can only delete individual words, not sets or a number of words you don't want or which are wrong.
If you think you can remove the whole language to get rid of the wrong word sets and reload good ones, you're out of luck, too. The option to delete the language is there, but you cannot click it - maybe this is a "special feature" of the paid version, but how can I know??? In addition, I am afraid that also in the paid version the words will not "remember" that they belong to a certain downloaded word set (it would be easy to implement this as a tag). I will not spend money for a program that I cannot test in real-world use.