This is a very polished to be called simple although simple is subjective. I've been developing language learning tools as a hobby during my programming journey, so it's great fun to try new stuff.
Problems...
I opened this in Hews2 Chrome browser and it got stuck on the "say the word" part. You might want to add a skip button there.
The sound effect audio is about twice the volume of the narrator audio.
Overall, it's great looking and engaging, even for an adult.
Questions I would like to ask but I understand if you don't want to answer.
I tried the Finnish language. Was that an AI voice? I just can't tell anymore.
What stack did you develop the front end with? How did you like it?