It’s a wonderful thing to do. Great for realising how much you are progressing. Fabulous for making your language learning feel “real”, wonderful for picking up the rhythm and flow of the language. Terrible as a way of picking up vocabulary. Why? Because it is brutally time in-efficient as a way to do that. Obviously, I am now addressing our target market, specifically individuals usually quite successful with little time to spare. If you have lots of time to spare – read. It’s good for you.
The trouble with using reading to increase vocabulary is that 50% of all the words you’ll read are made up of the most frequently used 100 words (approximately – it depends on the language but the principle remains the same). So if you read 100,000 words at an average reading speed of 250 words per minute that’s getting on for 7 hours. And you just wasted 3.5 hours of that time because you will be “over-learning” that first 100 words. Is that it? Not so bad. Unfortunately, it gets worse. Of the remaining 50,000 words you probably won’t want to learn half of them and those that you do want to learn either appear more frequently than required or less frequently than needed. Only a thin slice will be retained through reading alone.
To summarise – I think reading in a foreign language is a great way to track and validate your progress; it’s a lousy way to expand vocabulary. So, if time is important to you – use reading sparingly and mostly to give emotional support to your language learning efforts and therefore maintain your motivation.