I cannot recommend it any more highly. I use this very often for my own French learning and it's really helped me building my vocabulary and it makes the process of learning so much easier because I'm not copying and pasting into Google Translate all the time. So have a go at Readlang.
I speak 7 languages and I've used most of the language learning tools available so it doesn't happen very often that I discover something new that I'm genuinely impressed by. Readlang is one of those times! It's well designed, has just enough features, and is incredibly effective.
Readlang.com got me from near zero ability to read Spanish to, I'm guessing, intermediate or higher reading comprehension. I just kept going and going, not stopping, using readlang's interface to look up words and phrases on the fly, trying to make quick associations in my head with interesting words.