Starting a startup to replace Google Translate wouldn't be a simple proposition. Google's translation algorithms are considered best-of-breed and involve highly sophisticated statistical machine learning trained over a significant portion of their web crawl corpus data. Their staff scientists and engineers working on Translate are some of the best in the field, and the complexity here should not be underestimated. That said: yes, there's very obviously an opportunity here for the right team; but that opportunity is so big, its been there this entire time, even with the Google Translate API around.
Right... Some problems are fine just throwing resources at them, some problems need experience and knowledge, and in my opinion, you're not going to get the intellectual capital you really need for something like this, especially with a lean startup, unless you are the intellectual capital.
I wonder how much work it would be for Google to build a "Translation appliance" people could buy? I'd wager they'd do $100million in government sales alone the first year.