I am learning French, and so my answer will be based on that plus my experience with other languages. For starters I guess that the answer depends on what you mean by “feeling comfortable.” For example, do you mean comfortable reading? If it’s reading, do you mean reading technical papers (easier) or novels (in my opinion that’s the top of the ladder). Or do you mean listening? O speaking? Or writing – most definitely the hardest one, I think.
Back to French, my first language is Portuguese (and this matters since I can pick up a lot of French words simply because there is a Latin equivalent in Portuguese), and with a 10k count on Lingq I can read technical books and scientific papers with ease, but with novels there are a number of words in each page that I need to look up. That said, reading novels in lingq – which is the only place where I read novels – makes a it a breeze, and so interesting novels are one of my frequent weapons of choice.
As for listening, over the past couple weeks I was pleasantly surprised to find out that I can now understand most youtube videos talking about technical stuff (history, computers, geography, culture in general) unless the person is talking real fast. This wasn’t the case at all a month or so ago, and I am happily trying to find exactly what in the world just happened. One contributing factor might be that I keep listening to audiobooks with sentences and technical content almost non-stop: while driving, walking my dogs, etc. By no means I understand everything, but I just plow through. Interestingly, I seem to be learning a lot by context, although that takes a real focus. For example, I can’t be doing something else that requires attention (like writing) and listening to the audiobook. This might have been the source of this new and welcome youtube skill. Now, when it comes to audiobook novels, then I am definitely not there yet. I will certainly pick up words and expressions, but for the life of me I just can’t follow the narrative. My guess is that in listening to a novel there are often key sentences that you necessarily have to understand, otherwise the next one page gets lost in translation. For example, in a thriller all of a sudden the detective says a single sentence about a previous investigation, and then starts describing that investigation for the next page or so. If I miss that key sentence (as I always do), everything over the next page or so will get confused in my mind because I lost the transition sentence and kept thinking that the author was still talking about something else. Anyway, my current expectation is that one day my “novel understanding skill” will knock on my door, but for now I just keep listening and reading more and more.
One final comment, and here I think I differ a bit from the mainstream lingq philosophy - vocabulary acquired through reading matters a lot, no questions asked, and will contribute toward the other skills (listening, speaking, and writing). That said, if you really want to learn how to listen, you’ve gotta listen, and listen a lot. Same for speaking and writing, you’ve gotta actively practice the specific skill if you want to make progress, reading alone won’t fully translate into those other skills.