Vokabel is a free vocabulary-training program for both Windows and Android. Just write the words you want to learn and let the program test you. Almost all languages are supported, also languages that use non-Latin characters like Japanese and Russian. The program has intelligent functions that help you focus on words you don't know so well. There are many different test you can do (why not play a game and learn something in the same time?). All this to make the usual bore homework more fun and efficient. Enjoy :-).