If your target language happens to be Chinese then you can give it a try at https://reader.longyan.io/landing
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Related comment on another app: https://news.ycombinator.com/item?id=43769831
I also tend to believe to just convert between them is not the best approach. Better to find different content for both. If student wants to learn traditional script, they usualy want content from Taiwan and not from China, and the other way round.
There is no long-term gain from storing "hair" and "emit" under the same entry in your database. Storing 髮 and 發 separately, along with 发 as the simplification of both is a small effort now that will constrain you a lot less in the future. I've literally seen this pitfall happen with about 40 different Chinese learning apps over the last 15 years. Only a few (like Du Chinese and Pleco) got it right early on.