I just self-published my first book (http://survivejs.com/). Writing books is way harder than people think. Writing isn't enough as you need to tackle other aspects, such as marketing and sales, as well. If you are not native, you have the extra challenge of learning to write.
In short, it's definitely possible to earn a living out of technical writing. Getting started is the hardest part. If you don't have a reputation, you will need to build one. Growing audience will take time, but it will pay dividends.
To keep this comment short, I'll just link to a series of articles (and presentation slides) I've written about my experiences. Hopefully these help! Here we go: