Toucan is better for language learning. It replaces words in a page with your target language.
While I love the idea, I don’t trust the company with my complete surfing history. What they should have done is to have me opt into each website that I want to use toucan on and do not do anything if I visit others.
I guess you can already do this with Chrome's built-in translation, but that built-in translation leaves a lot to be desired, doesn't it?
So it's doesn't appear to even attempt show the grammar of the target language, including the very basics, such as the word order.
Even for vocabulary acquisition, how is one going to learn noun classes (genders), case endings and articles, things like German separable verbs etc?