Tucan actually works in reverse compared to Readlang. Say you're a native English speaker learning Spanish. With Tucan you browse the English websites you're already used to browsing, and it'll automatically translate some of the words to Spanish to sprinkle in a bit of practice that fits within your normal routine. It's a nice idea (actually this is the first one I saw doing the idea: https://www.theverge.com/2012/5/3/2995523/google-language-im...) but for me it didn't stick. I found it weird to be learning isolated Spanish words out of their normal context, and pretty soon it just became annoying to have these Spanish words popping up everywhere. Maybe it works for some people though.

With Readlang the idea is that you read actual websites in the language you're learning. If you're learning Spanish you might read El Pais or BBC Mundo for example. And to aid you, you can click on the odd word or phrase you don't understand to get a translation in English. It's intended for intermediate and advanced learners. Unlike Tucan you need to seek out texts to read in your target language, and Readlang offers a list of popular sites in each language to help you there: https://readlang.com/es/links, but there's obviously more friction than something like Tucan which fits into your normal English language browsing routine.