My experiment with taking on sponsors to pay for the costs of adding functionality didn't work. I'm fine with that though, as I was never really happy with showing ads for other people. So, I've swapped the revenue model – I think the last one earned around $20 over three years...
I've created an app, currently only on iOS, for Kana Bento. I paid Japanese voice actors for the audio. I'd love to make more games and apps related to language learning, and this is a fairly cheap test to see if the idea has any legs.