I went through the early parts of French Duolingo pretty intensively, but gave it up around the end of level 1, because it seems far too grindy -- not a good use of time. The part I did was good for bootstrapping to the point where you can start profiting from more real-life sources like the Harry Potter books.
The best setup I know of is an e-reader with a good dictionary configured to pop up on tapping a word. You can also select a passage for auto-translation, which is usually better than nothing. I use the Kindle reader on the iPad the most.
(Although it's good enough, it could be much better: the French dictionary lookup consistently swaps accented with nonaccented e's, the translator goes to Bing instead of deepl.com, the French->English lookup (which pops up in parallel) forgets at least half the time that the source is French and displays a useless null English->English translation of an actually French word. Going beyond the minimum, why couldn't we align a human-translated edition if you've bought one, or found a public-domain one? And the same for an audiobook of the same text? There's so much room to do these things better, not just for Duolingo. I blame DRM and the intellectual-property status quo to a considerable degree. I'm a little ashamed to be plugging a DRM-promoting setup here.)
There are some webapps and iOS apps for parallel-text reading, but last I looked the execution wasn't very compelling to me, and for me the time when parallel texts made the most difference is past. (Also, you learn that translators often seem to want to exercise excess creativity, or misunderstand things. This counterbalances their still-better-than-Bing general skill.)
To make the jump early, assuming you can enjoy them, see if you can find a wide selection of children's books from the library. It was kind of a nostalgic experience -- I'd forgotten what it felt like to be running into puzzling words and expressions all the time. This way is not so quick for dictionary lookup, though.
