Perhaps not in entirely text based games. However, all knowledge can be inferred, so theoretically, yes, you could. But you may find you'd learn better if you were to continue studying Japanese from a book, displaying what words mean to you. Or, when you have a guess for as to what words mean, you could keep a Japanese-English Dictionary with you, and check your work with it. Then, later, study from the text-book you are issued. That is THE most effective way I could imagine learning a language.