WHOA! How freakin' cool would this be on Google Glasses when traveling abroad! Everywhere you look... the text is just translated for you.
More than that, microphone + reasonable speech recognition = everybody you talk to is instantly subtitled. Also an extremely difficult problem, but one I'll bet will be commonplace in 15 years.
Because there is no way you could accurately subtitle German in English, other than knowing what he is going to say before he say it.
At one time I am sure there were people that said, "Mr. Wright, there is no way you can get that thing to fly."
Learn the difference between what cannot be done and what is impossible.