You don’t just have take our word for it, here is what Google has to say about using their tool for localization:
We recommend that you do not allow automated translations to get indexed. Automated translations don’t always make sense and they could potentially be viewed as spam.
One obvious question that arises from this warning is, why would an automated translation appear to be spam?
Think of it this way: Google loves to see lots of well-written, valuable content on your website. In fact, the search engine will reward you for writing it on a regular basis. Knowing that this is the case, you could very easily game the system with a tool like Google Translate. Simply write one version of your web page in English, and then reproduce it in 30 other languages. That’s 30 additional pages, but you only had to write one!
The problem here is that automated translations are not well written. They often come across messy and difficult to read. It damages the perception that potential customers have of your brand, and worse, it pollutes the web with mediocre content.
Google wants to make their index full of helpful, well written, unique content for people to find across the web. Their recommendation to anyone who wants to expand their website into multiple languages is simple: have a trained human being do it.
If You Must Use Google Translate
If you can’t resist having your website moderately accessible in another language, and insist on using Google Translate, there is a way to get away with it–but you won’t be able to have your cake and eat it too. To avoid any potential harm to your website , you can tell search engines to avoid crawling the pages that you have translated automatically. Just follow these instructions to edit your robots.txt file.
However, the trade off is that these pages will not be indexed. In other words, you will receive no SEO benefit for these pages in other languages.