Learn A Language By Reading
The best way to learn a language is to read it. If you're short on vocab, that might be difficult. Unless, it's manually pop-up translated. No slow select-the-word-wait-and-see-half-translation, I mean immediate and correct pop-up translation. That will allow you to go through texts fast. Reading is the best way to learn new words as you encounter them as part of a story, which is the natural way for your brain to retain information. In fact, the "retention factor" also has to do with the number of times that new information is "met", and the interval between "meetings".
Learn High Frequency Words
The easy words which occur most frequently in the text, you would have to practice ad nauseam in a regular course. However, when reading with pop-up translation you are sure to encounter those words enough times in the text itself to retain them in your memory. You just pick them up reading. So you save a lot of time. The Bermuda Word software that runs the e-books will support defining a word into high or low frequency and because the software knows which words are high frequency, you don't need to test these and you will retain them in your memory just because you will meet them enough times in the text.
Learn Low Frequency Words
Words that are more rare are difficult to pick up just by reading. The immediate pop-up translation makes it easy to go back and reread a bit of text which you now understand most of because the ease to learn high frequency words, and which helps to learn the low frequency words as well. On top of that, the software will calculate the occurrence of words in the text so that it will make you test the remainder of times.