I recently added some fiat currencies alongside USD to the Satoshi Bitcoin Converter app.https://satoshibitcoinconverter.com/https://m.stacker.news/14640
Good mate! Keep doing your work, it matters
What exchange rate are you using, Central banks or Parallel Market?
Not sure how to answer about central banks or parallel market, but I'm using the API of CryptoCompare.com for instance, the euro price is being accessed at https://min-api.cryptocompare.com/data/price?fsym=BTC&tsyms=EUR