I don't think it's a mistake. Non-subscription without clear gamification and engagement tricks seems like Rosetta Stone basically and that's the longest-running, most effective language learning software I'm aware of. When I joined the Army 18 years ago, while waiting for school assignment, I had the opportunity to train provincial reconstruction teams as a role player and had to cram learn some reasonable level of conversational Pashtun and that was what we used, before smart phones were widely adopted. The only real innovation I've seen since then is conversational LLMs that allow you free-form practice without a human partner, but even back then, scripted conversational practice was pretty good as long as there was a wide enough diversity of scripts.

Problem is more along the lines of "solo developer" here. Hacker News seems to have a real thing about this niche for whatever reason, but when doing something like this that I think requires real expertise in a wide variety of subjects that aren't software development, I think you need help. There's no way something like Rosetta Stone was developed without the input of experts in language learning and teaching, for instance. Knowing the platforms, programming languages, frameworks, and app store onboarding and delivery processes is already a lot for one person, but expecting to know the target domain on top of that is expecting an awful lot from yourself. I don't think it's a great sign trying to crowdsource business strategy from a free web discussion board, as a single example. This is the kind of conversation you want to have with your private team of people you know for sure have the experience they claim to have, not anonymous comments.