Language learning apps are the ultimate sand-pit for solo developers thinking they can offer some random unique feature that Duolingo (or "Anki but better") doesn't offer. Without realizing, they don't do it for a reason. Language learning has extremely low activation and retention. And it's super easy to find one or two early adopters that like your app for some reason to keep going.
And solo developers that get into language learning often are only strong in software development and lack in UX, design, product, or marketing.
You may start with a calm, "not Duolingo gamification" style app, but every language learning app starts with pure intentions until you're many months or years in, your numbers are low, you need to make money, and you need to move the needle.
My two cents, you don't have to heed it obviously.