I read on Kindle e-book reader. It has a dictionary function, and I can easily look up the unknown words without interrupting my reading. 

Видеть незнакомое слово - это все равно, что видеть на вечеринке человека, которого ты не знаешь.

Если на каждой вечеринке присутствует один и тот же человек, в конечном итоге вы захотите узнать, кто он.

Если слово появляется часто, это хорошо, чтобы узнать значение.

But that's the point in reading a book in your target language. Sometimes you can understand an unknown term because the context gives you the idea, but if the word is constantly repeated then you should look up the meaning, so that the next time you see it, you'll easily remember it and therefore you'll have added up to your vocabulary. Keep on the good effort!

When learning English, a dictionary is needed, not only to learn the meaning of a new word, but to learn the proper pronunciation too.

If you can go the extra mile, you can add the new word or sentence to your Anki deck.

In my case, I only look up the meaning of words, which I have never seen before, when those words or expressions look interesting/cool to me, or when I find same words more than twice, which means that such words might have a vital role in a story, and without knowing the meaning of them, the reading experiences might not be as pleasure as it’s supposed to be.

Each author has their favourite word choices, so it is also a sign to motivate me to have a look into meanings of them even though it is a little bit distracting the flow of ides; otherwise, I simply ignore unknown words, and indulge myself in a pleasure of reading.

Happy reading!