Hi kantord, congratulations on the site! I tried something similar about 10 years ago, called wikibabel. I then joined with another site called wikiotics.org. We were very focused on libre everything. In the end, we gave up after several years, but our content is still up and we've been looking for a new home for it. Please take a look and see if any of it would be useful for you (we had built a bunch of cards very similar to your demo lesson). We had stuff in a few dozen languages, including audio recordings (mostly of low quality). I've moved on, but I still love the goal, and would be happy to share some feedback on the experience if you want (contact on my profile page).

In short:

- focus on what the user wants, not the tech.

- is English->Spanish the best language pair to start with? You're directly competing with the giants like Duolingo. I tried to learn Burmese a few years back, I would have loved to find something like this for that niche.

Good luck!