Would this be possible?
How about a tool you can install on your web browser that replaces words on the webpage with words you've learned on duolingo? For example, reading a sentence on Wikipedia with French turned "on" might look like this: "...and developed a theory of couleur based on the observation that a prism decomposes blanc light..." with the words 'colour' and 'white' changed to French and a different colour or something. Obviously, this might only work for vocabulary as syntax will differ between two languages. Any thoughts?
No, it wouldn't really work because French is different than English. Those examples work, but what about other words? It would work as "the bread black." or, "I had eating an ice cream cone." Also, it would be difficult to make an app that could take the information JUST from Duolingo and make it possible to translate EVERYTHING, EVERYWHERE, EVER. Just sayin.
My friend's computer has something similar to this, from English to Chinese. When she hovers her mouse over an English word it shows the Chinese equivalent. I'm sure it could work the other way around.