To help you understand what's going on behind the scenes, NY Times published a massive long-read about how Google used AI in this instance, and how machine learning is reinventing computing itself. You can read the piece over here: The Great AI Awakening.
The paper notes that the effort took just nine months to complete, which is a lot faster than Google's own engineers expected. By adopting machine learning, the Google Translate service booked as much progress as it did over the past ten years combined.
At the moment, the improved version of Google Translate is exclusively available for English, French, German, Spanish, Portuguese, Chinese, Japanese, Korean and Turkish. Google plans to roll out the new AI-base system to abut eight new languages each month, meaning the entire effort should be completed by the end of 2017.