When I started learning more languages as an adult, I found that the biggest accelerator for me personally was likewise to read novels, even if they were way beyond my nominal skill level. The first 50-100 pages would be slow grinding, looking up almost everything in the dictionary, but then it would rapidly get faster and easier as I got used to common turns of phrases, idioms etc. And it was great for maintaining real motivation, wanting to read and understand these captivating stories by Eco, Houellebecq, etc.