Curious because I’m trying to learn Romanian, and since it’s a less common language there are fewer resources available. So I wasn’t sure if you added Dutch with minimal amount of effort following the poster’s request.
That said, I gave your app a try with Spanish and it looks pretty good! But I didn’t see a Help page to clarify how I’m “supposed” to interact. Eg I tried saying in English “I don’t understand” (even though I know how to say that in Spanish) and it responded in Spanish which may be hard for absolute beginners. Although full immersion is much better way to learn.
I can try playing around more with it to give you some feedback.