I gave up on Harry Potter in Dutch and spent almost nine years building a reading app
In 2016 I moved to Amsterdam for a job, and by 2017 I was learning Dutch. I had done over a year and a half of Duolingo, tried Memrise and Babbel, gone to evening classes and some meetups, and I had stopped making progress. So I tried to read Harry Potter in Dutch, with the paper book in one hand and Google Translate on my phone in the other. Every word I didn't know meant unlocking the phone, typing the word, spelling it right and finding my place on the page again. A page later I would look up the same word, because I hadn't kept the translation anywhere. I gave up after a couple of pages.
I got the idea for Simply Fluent from those two pages: a reader where you translate a word without leaving the page, and where a translation you save is still there the next time the word comes up. In 2017 I prototyped for a while to check that the technology could do what I wanted, and in 2018 I started building properly. I had never built an app. I'm Marco, and I have funded Simply Fluent myself from the start.
Learning Dutch by testing my own app
Building the reader took all my free time, after work and on weekends, so I had no time left to study Dutch. But every evening I read a few pages to test the reader and find bugs, and after a while the reading was the reason I opened the app. I finished my first book in Dutch, then a whole stack of books. Later I went on a walking tour given entirely in Dutch and understood the guide, and I could watch films without subtitles. The app had no audio back then, so all of that came from reading.
Since then I've read books in German, Spanish and Portuguese the same way. For Spanish I learned the first couple hundred words with flashcards and after that I only read. Four months after my first Spanish book I spent about two months in Ecuador and then five weeks on my own in Colombia, getting by in Spanish. I started Portuguese about three years later, from zero with only my Spanish. My first book in Portuguese was 300,000 words long and took me 26 hours of reading. So far I have 229 hours of reading in Spanish and 150 in Portuguese.
I'm not a language teacher, and I don't call myself a polyglot. Reading a lot of books worked for me, and I want the same tool to be there for anyone who wants to read in the language they're learning.
What you do in Simply Fluent
Simply Fluent is a reading app for language learners, on iPhone, iPad and Android. The main idea is that you bring your own books and read what you want to read. You import an EPUB, PDF, TXT or Markdown file, or paste in any text. If you don't have a book yet, or you don't know where to start, there is a library of short stories and classics rewritten in modern language, graded by level. You can read in 45 languages and get translations into 134.
While you read, you translate any word or phrase and get the meaning it has in that sentence. You see all the meanings of the word, with the meaning for that sentence highlighted. If the word is part of an expression or an idiom, the expression is detected and you get the meaning of the whole expression. Next to every translation there is a lightbulb button. Press the lightbulb and you get an insight: what the word means here and, when there is something to say, what else the word can mean, a grammar note, common word pairings and example sentences.
The feature I wanted most back in 2017: save a translation and the translation is shown above that word or phrase in every book you read in that language. Once you know a word, mark the word as learned. The translation above the word is hidden, the word stays highlighted, and you can still open the translation if you forget. Every translation you save also becomes a flashcard, with spaced repetition.
You can have any book read aloud, offline, with the voices on your phone. For languages with another alphabet, there are courses where you learn the letters a few at a time, for Russian, Hebrew, Greek, Ukrainian and Korean. For some languages there is also a deck with the first 100 words, for the weeks before you can follow a page.
The rebuild in 2026
The first version of Simply Fluent in the App Store and Google Play wasn't good enough, for me or for the people using the app. I was building and marketing the app at the same time, on my own, and after launch I was always rushing to add whatever people asked for. I patched for a long time. Patching while doing the marketing and keeping everyone happy was wearing me out, and with the way the old app was built, every new feature took far too long.
I also stayed anonymous for years. I tested the app with people in person, but my name wasn't on Simply Fluent and the people using the app had no way to reach me, so I had a hard time knowing what was working.
In builder communities on social media I saw how much care other people put into their animations and interfaces, and I felt Simply Fluent deserved the same care. So in February 2026 I stopped adding features. I took screenshots of every screen in the old app, more than a hundred of them, and redesigned every one, from the first screen you see to the last setting in the reading screen. I wasn't happy with the result, so I redesigned the style again, and then a third time. Then I rebuilt the app on top of the new design.
Version 2.0 came out on 28 September 2026. Version 2.0 is a new app with the same name and the same idea, and this time my name is on Simply Fluent. Every translation people saved in the old app carried over.
What I changed in 2.0
Pricing
In the old app the free version had daily limits, with separate counters for translations and insights that reset every day. With a daily counter, people start rationing their lookups, and someone who is rationing lookups isn't reading. So I removed the daily limits. Premium now has a 30-day free trial, and there is also a limited free version: the whole library, saved translations, flashcards, read-aloud, offline reading, one book of your own, and 150 translations and insights in total. Translations and insights during the trial don't count toward the 150, and inviting friends adds more. Premium is $6.99 a month or $49.99 a year in the US, with no ads.
No account to start
You pick your language, answer a few questions, and a moment later you're reading. You can try everything in the app before you make an account.
Streaks
I held off on streaks for a long time, because I didn't want people opening Simply Fluent to keep a number going more than to read. But several people asked me for streaks, some of them in person, and it's not up to me to decide how you like to keep yourself going. So 2.0 has streaks, achievements and a statistics screen. Reading, flashcards and letters lessons all count for the streak.
Fixing translations
If a translation is wrong, give the translation a thumbs down and I fix the translation for everyone. I see every thumbs down, and I read every message that comes in through Support in the app. A lot of 2.0 exists because people who used the first version wrote to me about what was broken and what was missing.
What I want
The goal is the same as in 2018. I want people to get to reading sooner, in books they picked themselves, so that one day you can pick up a book in a library, in the language you've been learning, and not need the app at all.
Simply Fluent is on iPhone, iPad and Android, with a 30-day free trial and a limited free version, and you can try the app without making an account: simplyfluent.com
If you're building an app on your own, or you're learning a language and want to tell me which book you're reading, write to me through the contact page on the website.
