I think that most of the time a word-for-word translation is enough. I use Google translator a lot, and most of the time the translation is not perfect but it is good enough. So I think that is app is very useful.
But I think that the real problem are the idioms and phrases, like "dead end", that have a completely different translation.
On the other hand, I think that you have more processing time that 1/10 sec. Most of the time the user will point the app to the same text for 10 or 15 seconds. I think that it is possible to show first a very fast translation almost instantly and a few seconds later show an improved version.
Some times, but not always. Not even sure if it's "most" of the times. "Right turn" to "correcto turno" is so wrong, anyone following directions with that would be lost pretty easily.
Still, amazing technology, specially since it's all client-side. Hopefully they'll have some contextual analysis in the future or enable Google Translation API use.
I know that Google Translate is not word-to-word, but it is not perfect.
For example, a few years ago, some students of my wife give to her a homework about clocks and gears. When she read it, she was annoyed because the redaction was incredible horrible. But later we realized that the students didn't write it, the "homework" was a web page translated with Google Translate.
Another time, I need an example of the differences between JPEG and JPEG2K for a internal talk. I found a photograph with a zoom of Lena's eye with a legend like "JPEG2K 1% vs JPG 1%", but the webpage was in Japanese, and I can’t reed it. So I use Google Translate to be sure that it was a comparation of the two methods with the same compression level.
So Google Translate is very good to get an idea of what some web page means, but it is not good enough to make a final version of the translation.
This app have some additional difficulties that GT doesn't need to solve: they need to OCR the text in the wild, they have less computational power and they have to do it in real time. It is almost incredible that they can solve these things. With a word to word translation, I think that you can get a good enough translation 90%, 95% or even 99% of the times, but the corner cases can be really unintelligible. The translation of "Tongue Bolivian ..." is fine, and the user can understand what it means, so it is useful. The translation of "Dead End" is something that they should improve in next version.
I once saw this forum post that was in German, that Google translated "A: Nyet." to "A: Yes."
Since it was a question and answer post regarding information for an upcoming game, there was quite of bit of fuss over it before this translation error was discovered.
But I think that the real problem are the idioms and phrases, like "dead end", that have a completely different translation.
On the other hand, I think that you have more processing time that 1/10 sec. Most of the time the user will point the app to the same text for 10 or 15 seconds. I think that it is possible to show first a very fast translation almost instantly and a few seconds later show an improved version.